Tax credit

Hi all
I have got a letter from the tax credits claiming I owe them £3295 due to the fact that they had me down as income based esa not contribution based esa I have spoken to them and I have to go through a appeal process.
I am apparently recieving both income and contribution based esa but slightly more elements of contribution based esa.
My question is I'm in the support group of esa and have been since my assessment in September 2016 and esa in total since may 16 2016 are they telling me the truth about not being on income based as it seems if everyone was on contribution based it would save the government loads and now they are taking over £100 a month back off my tax credits that I can not afford.

I was in work constantly for the whole 34 years prior to my claim.
I don't understand that when I first claimed esa I phoned up and told the dwp that I was getting esa it did not state on the letter which I still have wether it was IB or CB and I was not aware of any of the terms myself the dwp has put down IB and because or there error I have to pay back £3295 it's just so exasperating as they are saying "well after your conversation we put down IB so I must of told him" when the truth is I never even heard of the terms IB or CB at that time.
Now I'm told I'm getting both but it's slightly more CB than IB how convenient....