Lost information

Hi I don't know if anybody can help me but I had an ESA50 renewal form sent out to me in October which made me feel Ill from the minute it arrived,  my anxiety has soared through the roof since and along with many sleepless nights I contacted Disability solutions in my area who kindly filled it in for me, I then got various amounts of information together from different consultants and contacted my social for a copy of my care package as ai have care twice a day l, all this was also included. I posted this to Five Ways in Birmingham which was on my letter on the 19th November and by Christmas was worried I'd heard nothing, today I received an assessment interview letter and was devestated they'd need to see me after the varied detailed information they'd been sent, my conditions are very complex and I have severe anxiety disorder aswell so I rang them to ask why that wasn't enough only to be told they've received NOTHING back from me, not my form, evidence NOTHING AND they've contacted my OLD Doctors from over 2 yrs ago to which obviously they've had no RESPONSE! . The lady on the phone was pretty much threatening if I didn't attend I could have my money stopped but I'm not happy, they can't just brush off all that important stuff has been lost and luckily I have postal proof my documents were signed for on the 20th Nov and I'm definitely not happy being forced to go for a completely BLIND assessment .It took me AGES to gather all that stuff together, I'm devestated and some fools lost it ALL. Where does that leave me with my rights, Any advice please?