Tax credits overpayment, can i pay back instalments?

[FedupofTurkey]

I told tax credits the day my circumstances changed a year ago. Not heard from them then get a letter saying i owe hundreds and need to pay back in 3 weeks. I can't afford to do this, we struggle as it is. Will they be agreeable to an instalment repayment? How little will they take?

We are repaying £30 a month on a just under £1000 overpayment.
The person who I spoke to was very pleasant and said I could Pay less each month if it was going to be a struggle. I got the impression that they just wanted us to just start repaying something each month.

I sent a recorded delivery letter asking them to explain clearly how they came to over pay me, when I have always kept all my details correct and up to date. You are entitled to query it.

I have yet to hear back from them and that is months ago.