the phone has a serial no. etc and they SHOULD have records of phones sold n where so u may be ok ,
as for credit card statement aslong as u can prove u brought it there then they cannot dispute it , they may say u will have to send it to the company to see y its broke or if its repairable , then for the sake of £90 they might not bother but 1st find summit to prove u got it @ argos

Scott