Phone giving problems could be the network or phone itself.

Hi i recently got a contract phone from Telkom & in a few months the phone been giving my boyfriend problems as he's using the phone, can't receive calls or make calls at times. had settings done so that it could work but hasn't even called them yesterday to get answers they gave me settings to do which I've already done & redid it again & still not right, because of the phone giving problems was unable to get my emails on time for that reason my boyfriend missed out on job interviews & call backs which is so wrong. I need to know what I should do coz at this moment I want to cancel the contract coz its just giving problems & will rather go to another network that I know will be reliable. need someone to get back to me today regarding this matter please.