A Sony M4 Aqua and VERY bad serice

I upgraded my contract to a M4 Aqua, which has given me endless problems. After having the phone for just a month, I sent it in for repairs, however the problems are still present on the phone. Some of the bigger problems are that it freezes and I have to wait for hours until the battery dies before I can use the phone again, or it just loses the connection to the SIM card and I can not use the phone. What good is a cellphone which I cannot use? Videotronic in Grahamstown offered to send the phone in for software updates, which I can't see helping as I already took this route and it made no difference, it actually seems worse. Is it not possible that there is a hardware problem with the phone and not a software problem, like they are so quick to diagnose? So following their advice I took the phone into Vodashop in Green Acres today where I was helped by a very rude lady named Claire. She was kind enough to inform me that nothing can be done to help me because I chose bad phone, fantastic service, thanks Claire and Vodashop. I do not see why I should be stuck paying for a phone that most of the time cannot do what it is designed to do, make phone calls? And secondly, why should I pay for it when every second or third month I need to send it off for repairs for a month at a time? Surely there is something more that can be done other than tell me I need to be stuck with something that can't perform the tasks that it was designed to do, purely based on the logic that I chose a bad phone? Obviously, at the time, I was told by the salesman that this is a fantastic phone, that's why I chose it. Please can someone help me with what I need to do to resolve this, but its really not fair to force someone to pay every month, for a faulty device that they cannot use. Regards, Liné