Black Berry 9720 low standerd product

The phone switch itself off. When I switch phone off to pray and put it on report sometimes ' simcard error'<br> take battery out and in then phone works again. Sometimes 3-4 times battery open and close to get phone activated.<br> Sometimes get whaatsapp get report ' not enough space on file system, although 4 gig memory card installed<br> Not happy with phone at all and ask the phone te bereplaced with another or refund, but gave me same phone again via Hyper Home, Mayville