Pip assessor lied about telephone contact

Hello, I've written before as was due to be assessed on 18 June at 11am. I waited for half hour and while I was on phone to the PIP assessment office, the assessor phoned at 11.33am. I am now classed as missing this assessment and they (IAS, Atos) shockingly lied as said they phoned me 3 times, the latest at 12.40pm. My mobile phone shows I received no such calls but they sent this to the Dwp. They also said my voicemail was full, another lie. I only receive voicemails from my GP or brother about 3 times a month which I delete immediately. I am disgusted that IAS (atos) could lie so much. I'd love to take legal action against them for this. What can I do? I did phone DWP and was very upset but explained IAS were lying about those attempted phone calls. There were private numbers on my phone on the day 17 June before my 11am 18 June appointed but my phone is on silent 95% of the time and I don't answer unknown numbers unless I forwarded. Has anyone taken IAS to court for lying?