PIP home assessment

Hi everyone.
Could someone advise me on this problem I have please.
I recently filled in a pip review form, with the help of an occupational therapist, describing how my condition has deteriorated as the result of a road traffic accident.
I asked for a home visit again as I have had two home visits in the past.
Last Thursday I received a text, from Atos, calling me in for a face to face assessment at one of there assessment centres. I phoned them up and told them that I would need a home assessment again. They said they would cancel the appointment and would note that I had requested a home visit and they would seek further information from my GP.
Yesterday I recieved a letter from them stating that on the availiable information, ther health proffesional has decided that they still need to see me in person at a consultation centre and they would be in touch with me as soon as another appointment became available
I stated, on my form, that I had attended several hospital appointments, in a taxi and with the aid of friend,s and I think this is how they have reached their decission that I am capable of attending one of thier assessment centres.
What I neglected to mention was that I couldn't always fulfill these appointments because of mobility problems. My mobility has become worse since my last home assessment and I am a bit shocked that they can deem me capable of attending an assessment at one of their centres.
All my GP consultations, in the last 3 or 4 years, have been conducted over the phone because I can not allways fulfill appointments and I dont know how my mobility will be from day to day.
I am awaiting a telephone consultation, on Friday, with my GP and intend to ask her for a letter of support for a home visit but I am worried, that even if she agrees to my request, I will not receive it in time to submit it to the DWP before another appointment has been arranged for me by Atios. I am under the impression that I can only cancel one appointment, which I have already done, and that I will not be able to attend the next appointment they make for me.
Can anyone advise me on how I can communicate all this to the DWP.

Thanksi in advance
Ray

Thanks for the reply Gordon.

Just to clarify, do I telephone Atos again or DWP? Atos told me to send additional evidence to the DWP.

Hi Gordon.
Sorry to bother you again. In your previous correspondence you mentioned that I shouldn't cancel any replacement appointment that I am offered. Do you know what alternative I have?
If I can't attend an assessment, surely I must inform them that I can't attend.