Phone not ringing

Since I have had my contract (Sept 2013) my trouble started. CellC has replaced the phone to no avail. I would receive about 50% of calls. The last month CellC are trying their level best to to get that figure up to 100%. Yes I have only received 5 calls in the last month and about 15 -25 missed calls every single day. My phone does not ring but goes straight to voice mail. I think it is a **** as I have to phone these callers back for my own account. Can't wait for September to come so I can finally get rid of the worst service provider in the whole world.