Work Capability Assessment

My wife has had two supposed ghost telephone appointments with the DWP, on both occasions they never rang at the arranged time or day, as my wife and myself sat there waiting on the calls on both occasions. I lodged complaints on the DWP Universal credit Journal website on both occasions. "The letter was sent out on the 1st of March 2021, we received the said letter, on the 5th of March 2021, stating that an appointment having been previously been arranged for the 8th of July 2020 had been rescheduled. We had received no prior notice of this arrangement. Still, they arranged for a new appointment in this letter for between the hours of 9:00 AM & 10:00 AM on Thursday the 11th of March 2021". The second appointment came and went on the 17th of May again no phone call as we both sat there waiting.
Received 2nd letter for telephone assessment from DWP after 1st no show by DWP, letter dated 5th May 2021, Between 11.30 am & 12.30 pm for Monday 17th May 2021, Yet another no show by DWP." We, myself and my husband sat from 11 am until 1.30 pm no phone calls were received or made during that time period, the phone line was checked by BT and no faults found. I, Lorna's husband, is finding this whole episode distasteful, in that, the time between receiving the notification and the actual phone call, which never occurs is like a mind game, that is not helping my wife or her mental state as she is losing a great deal of sleep, not eating and becoming more irritable and inward-looking. I am aware that this is not your sole responsibility but you are all working for the same government department. I am placing notice here, in writing as to the problem we face and the increasing pressure my wife faces." We received a letter today 19/05/2021 threatening to stop our payments because WE FAILED to attend both phone Assessments this letter was dated 18/05/2021. Has anyone experienced this behaviour before and what is the procedure for it?