Backdated esa from contributions to income

I would like some advice, I was on incapacity benefit and the dwp changed me over to esa contributions in 2011 This year in May I received a letter saying I could be owed back payments to Aug 2011 as should of been on Income esa. Few days ago I received letter saying as I was with my partner at the time of 20 Augu 2011 I am not entitled to backdate but will give me it from this year from May when they sent me out a letter. My query is before I appeal as in the mandatory recommendation they said the same I told them that although in Aug 2011 I was married we separated in Nov 2011 and I informed the DWP who as change of circumstances should of updated my claim to Income Related esa this was their error not mine and as for the 20 Aug 2011 that is the day dwp found out they made the error. Could someone tell me should I not be entitled to backdate benefit from Nov 2011 when my husband and I separated then following year divorced. Why would they not pay me and is it right for me to appeal. If someone can help please reply as have couple weeks only to appeal. Thanks

Yes when I filled out the form and over the phone I stated that on the 20 Aug 2011 I was married but I separated in Nov 2011 so even if I wasn’t allowed the back payment from Aug 2011 I should be allowed from Nov 2011. I don’t understand why they are stuck with that one date. All the authorities eg child tax credit and housing benefit knew I had separated on the date in Nov. I would like to know are they right in refusing me or have I got grounds for appeal? As they have started paying me joe from May 2019 when I initially got the first letter. Thanks

Forgot to mention that yes my ex husband was working at the time but he moved out in Nov 2011 I was a single parent

Yes I got hold of the child tax credit people and they said it was on their system that I had separated in Nov 3011. Now I just want to know why there so fixed on that one date and not willing to pay me from the time I told them till now. Have I got grounds for appeal. I don’t know where to go for help on this as citizens advice is also baffled