TC956 form and disability element of WTC

It's quite long winded and rather complex Adrian but I'll do my best to explain.
I'm 59 yrs old, work 21 hours a week and have suffered with Fibromygalgia for many years which is getting worse with the chronic pain and fatigue and many other things that goes with it.
I was on Long Term Incpacity Benefit for roughly 18 years.  I was in an abusive marriage for 22 yrs and in the end got involved with a domestic abuse organisation.  After being with them for approx 2 years they asked me if I'd like to volunteer for a few hours a week.  I checked with the DWP and told it was fine.  Then a few years later back in July 2013 they asked me if I'd like to work with them on a part time basis as they knew I couldn't work full time.  Anyway I notified the Jobcentre that I would like to stop the Incapacity Benefit claim and they told me that I could apply for the disability element of working tax credits and told me what I would be entitled to.  So I sent off for the form which I believe is TC956 and I fitted the 3 criterias of A. Working more than 16 hrs a week. B. I couldn't work an 8 hr day or 5 days a week and C. That I had been in receipt of long term Incap Benefit 182 days before the claim.  There were no other questions on there about my health etc. They said I was entitled to the claim and having been paying me ever since.  Last week I found out that they had stopped my claim and when I rang them they said that it was because DLA had notified them that I wasn't entitled to it any more.  I did explain that I had never claimed DLA  before and wasn't registered as disabled only that I had filled the TC956 form in and had been in receipt of long term Incap Benefits.  
I've had to do a Mandatory Reconsideration letter and am waiting to hear from them but I'm so worried and stressed which is making my condition much worse.