What is the best way to contact Social Security regarding repayment of overpayment of benefits?

I worked a few years ago, while receiving benefits, not knowing if I had made more than the maximum income to receive benefits. SSA notified me about the overpayment after I was no longer working and reexperiencing medical problems. I sent them a payment, but they asked me to NOT send any more while they were reviewing my case. I have not received benefits since. I am finishing my education and expect to be employed soon, and would like to pay back my overpayment, if necessary. Can I just send them a letter asking for my repayment amount, or do they need lots of doentation of communications they have had with me about reconsidering my disability? What is the best address to contact them about this?