Atos Phone Calls

Can anyone tell me, can we ask Atos to write rather than phone up to make an appointment? I had someone on the phone earlier today which I think was Atos asking to speak to my sister (thought they wouldn't say where they were calling from). I said my sister wasn't available, the woman kept saying it was a confidential call when I asked her where she was calling from though gave a first name. When I kept probing she said she was calling from a 'health centre'. I thought it may be to do with a complaint my sister had made about a psychiatrist she'd seen but she didn't leave a number when she made the complaint. Neither has she directly given a phone number to Atos but they may have got it from the DWP or appeal documents.
This is post-appeal. She was already put in the WRAG group but appealed it to go in support and they adjourned the appeal to get more information and one of those was to have an assessment which she didn't have originally. So it could be that they are just making phone call to arrange a home visit which she has requested. But if they phone again should I just mention her fear of phones and for them to put it in writing with a contact number?
Are we within our rights to ask them to put it in writing? I have heard they do tricks to trip people up on the phone

I am not convinced about 'tricks' to try and catch people out, but it is true that claimants are perhaps more likely to get muddled when dealing with people for DWP/ATOS by phone.

You have every right to request that all communication from DWP/ATOS to your sister is conducted in writing. As you have seen, they are prone to ignore this and phone up anyway, but your sister does not have to respond to this. She will then be notified in writing - as requested in the first place!