Phone call from Capita after pip assessment

I had my pip assessment on the 18th April with Capita, it's now the 28th April and they've rang me this morning and left a number for me to call them back.

1. If they require further info - do I give them this over the phone or do I insist on sending them it by Post? this is unlikely as I sent loads of up to date info form GP, Psychiatrist etc

2. If they say I haven't qualified do I ask them for an MR during this call?

I've obviously no idea what they want, could you play devils advocate for me please as to what they might want or do? and my do's and dont's.

Forewarned is forearmed.
Thank you.