ESA50 form missing

my wife received a esa50 review form to fill in, they wanted it back by 1st Sep, we rang them on 25th Aug to say the form would be late as due to wife's medical conditions such as bipolar, depression and being suicidal, we was told that fine as long as you explain on the form why you are sending it back late there is no problem. we sent the form back by registered post to Wolverhampton as the envelope stated and we have the name of the person, their signature, time they received the pack, and reference number.
we received a letter from them saying we have stopped your claim for ESA due to form not being sent back, we had no warning this was going to happen just got the letter, when we rang them they said it our fault as the form was sent back to late and was not received by the deadline, we was not told about a new dead line for the form apart from the 1st Sep, and we rang them on 25th Aug saying it would be late, the reason they have given us is that they don't have the form in their computer system as from the 25th Sep, but they received the form on the 18thth Sep, and their reply was you did not allow 21 days for the form to be put onto the computer system and have stopped all our money including housing benefit council tax so far that we know off, we rang them on Friday 29th sep and after days of calls and all different people and areas that we spoke to we was told as this is your fault the form was late you may stand a chance of getting the form up to your nearest job centre and ask them to scan it directly into the system which we did but we had to beg and cry for them to only do the form and not the extra information over as they would only send it internal mail which don't help us as the information wont be on the system either, so we spoke a lady today and she has said again because it was your fault we did not receive the form back in time it has to go to the decision maker to see if they will reopen the claim and we wont receive any money until this has been sorted, can anyone out there help me on tis matter, can they do this when the form is with them in the first place, stop our money, cancel the claim for esa and put the blame on us without telling us that the form needed so many days in their hands before it goes into the system when there is proof they have received it, also can they put her on job seekers when they are at fault and not us, we need as much help from who ever can help please sa my wife has tried to kill herself twice in the past week from this added stress on her and she cant be by herself for no amount of time, hope someone can help me.