Pip just stopping my money

I received a part payment when I called up the first time they said computers where down call back in 2hrs, second time I got through got transferred to a claims manager, he said they had sent me a assessment letter but I had not returned it in time.
I told him I had not received a letter, he said it should have arrived on the 20th which would only give me about 10 days to fill it in.
I told him I had not received the letter, which he said that will be fine I will put down good cause for not returning did not receive, at this stage I was in a state he asked me if this would cause me financial difficulty he did not offer to reinstate my payments, which i replied I just want it sorted out (did not want to owe money to them if unsuccessful but did not say that to him,) so he told me it would take about 20 days to send me a letter out was that okay I did not know what to say and in a state so said okay.
He never reinstated my benefit and I got a text saying you have asked us to review your case which I didn't and we will be in touch within 8 weeks, now I am worried that the will just ignore me and not pay me for 8 weeks then time is up and do not know what to do.
Should I recall them tell them 20 days is not alright and to reinstate my money as they have stopped it with no fault of my own, should this also be followed up by a recorded letter. thank you