PIP timescale

Advise please...
I asked for my PIP to be reviewed because my medical stituation has changed. 
I sent my application on the 3rd of of January and I sent in further reports from my GP and specialist at the end of January. Mybtracker said they received it on the 10th of February,  DWP said they recieved it on the 26th February. From then on every week I would call up to get an update, I know a lot of people suffers severe anxiety so they knows exactly how it feels. I don't just have mental health problems I also have physical health problems which is why this is a big deal. Every time I call I get different update..."that I should hear soon" or "they have until 13th April" to give me a decision. Today I called up and DWP gave me a number to get an update from the assesor, I called them up and apparently they have only recieved it on the 11th April and because they never have a record of me as an existing one. At this point my anxiety heightens and explained to her I do not understand why they didnt have a record of me as they saw me for an assessment over a year ago. They asked me if it's definitely with them, I said yes otherwise I would not be able to tell her exactly where it is (I wasn't shouting because i respect that they are just doing their job I just explained). She said at the moment my form is being treated as new because they do not have a record of me and it is on the scrutiny stage. I said thank you and ended the call and I cried. If my anxiety didnt get the best of me, I would have liked to ask her what happened to my previous record when I attended their assessment centre? Which according to them they NEVER had a record of me attending the assessment. Are they being careful with everyone's record? And why have they only just got my form on the 11th April? How long until I actually get an answer. I feel miserable, I can't breathe because of my anxiety. Please help and assure me that DWP are being careful with our records