Hi ,something similar happened to me 3yrs ago,they overpayed me when I was off work ill,but because I went out and got myself a job I was told I had to pay £2310-00 back because they had overpaid me,because of my other money commitments they agreed that I could pay it back at £20-00 per month which I am doing and the direct debits finish in the year 2016 2years after my retiring age,It would have paid me to have NOT gone back to work.But the moral of my story is just offer to pay it back so much a month so you can still recieve your full benefits.