I got to page 3, so apologies if this has been mentioned.
I used to work for hmrc in their debt management telephone centre. I was the person you phoned to talk about an overpayment of tax credits, unpaid self assessment and paye etc.
Those people have no idea how your overpayment came about, we don't get told. We can see where it came from, i.e the award year, but no more. The tax credits helpline and powers who be do not pass that information on. Please don't be angry at them, we know it's a shit situation and we know we cannot explain why and you've been passed from pillar to post. Many a time I was upset after a call because things are so awful for some people and I felt powerless to help, bar pass on another nunber and note down what you told me. At the end of the day, the people answering the phone are just doing a job.
I will tell you though that you can request a payment plan and it does not need to be 2 years etc. You can dispute it. If the payment arose from a joint claim and you separate then you are only liable for half and if you pay your half off and they still contact you, go as high as you can as it is not your responsibility- joint claim means joint liability.
I claimed tax credits and ended up with two overpayments. One I paid half of and was caused by me moving in with a partner: I stopped working, our household income dropped and we went from 1 child to 2 children in the house. Yet somehow they overpaid that.
The second time I was a single parent, I began employment and told them asap. My overpayment was more than my months payment.
I paid both by a payment plan at £50 a month. Don't let them tell you it isn't possible, and don't let them bully you in to an anount you cannot afford. Request an income and expenditure (it can be done over the phone). Advisors cannot take more than you can reasonably afford.
I'm done with tax credits forever due to the hassle.