Paying back retirement withdrawn

Q: I withdrew my CSRS retirement in 1993 and then started back in the government in 1999 and was hired as a CSRS offset employee. My service comp date is October 1981. I also have years of service from 1977 to 1981 and then came back in 1982 and worked until 1993. I resigned in 1993 and went back into government from 1994 to 1995 and then resigned again. I then came back in the government in 1999 and I am still working. I am a CSRS Offset who unfortunately withdrew my retirement when I left in 1993.
I asked for the figure I had to pay back around 2001 and the approximate $18,000 had grown to approximately $34,000. I initially started paying back $200 a month and then increased to $300 a month. I was getting statements of my balance and then the summer before last I was told we would not receive statements anymore. Then I received another letter stating that the taxes were not withheld for a period of time, so $5,000 was added on to my balance.
Then I got a letter a couple of months ago which said they had fixed the problem, and we would get statements again by April 15, 2010. This letter said the amount for some peoples might go up and others might go down. Well, no statements arrived, so I called OPM and was told to send an e-mail to screceipts@opm.gov with my CSD number on it and I would get an e-mail back.
I am concerned about that accuracy of what I owe, and I do want to pay it all back, but it is so convoluted. When I called OPM and asked how they came up with the $5,000 figure, the woman could not answer me.
Does any other CSRS Offset have the same problems?

A: Here’s the explanation and instructions that OPM will soon post on its website:
Service Credit — Frequently Asked Questions
Background
1. When was the interest problem discovered?
Errors in the computation of interest and consequently, incorrect balance amounts on receipts, were discovered in 2008, which led to the July 2008 shut down of parts of the system.
2. What is the issue that created problems in the calculation of interest?
Interest on pre-October 1, 1982, deposits and redeposits under the Civil Service Retirement System (CSRS) is fixed at an annual rate of 3 percent and accrues daily. Interest on post October1, 1982, deposits and redeposits under both CSRS and the Federal Employees Retirement System (FERS) is variable and accrues annually. In some cases, interest was applied at the variable interest rates instead of the fixed 3 percent rate, which caused the interest to be understated and in other cases, the reverse happened, which caused interest to be overstated. There were also some instances where interest was not charged at all for the year which also caused an understatement of the amount due.
3. Why has it taken so long to resolve the problems with the Service Credit System?
It first appeared that the erroneous statements and other errors resulting from the system change could be quickly resolved; however, during the same time period we lost key programming staff which significantly slowed corrective efforts. In addition, a number of other posting issues surfaced during this period that needed to be analyzed, resolved and tested. This effort further contributed to the delay in restoring the system.
4. Is it possible that some account holders will have to pay additional interest and some will be getting a refund?
Yes. It is also possible that some account holders with a mix of pre-October 1, 1982 service and post-September 30, 1982 service, who have deposits and/or redeposits have overpaid interest on one type of service and underpaid interest on another type of service.
5. How will I know how much I owe or if I am due a refund?
OPM will prepare and deliver corrected statements to all active account holders showing whether you owe additional monies or if you are due a refund. We will post additional FAQs relating to the information on the corrected statements when they are sent.
Statements
6. How do I obtain an updated statement until the Service Credit System is fully functional and new statements are sent out?
Receipts cannot be provided until OPM has completed updating and has fully tested the Service Credit System, which is currently underway.
7. When will I receive my next statement?
You will receive a current statement as soon as we finalize the testing and conduct a reconciliation of all affected accounts.
8. How do I obtain a paid in full receipt?
Until the Service Credit System is fully functional, please send your request by e-mail to screceipts@opm.gov and a response will be returned by e-mail. Be sure to include your name, date of birth and CSD Claim Number.
9. How do I find out what my “balance due” is until the Service Credit System is fully functional and new statements are sent out?
Send your request by e-mail to screceipts@opm.gov and a response will be returned by e-mail. Be sure to include your name, date of birth and CSD Claim Number.