Poor Service

For the past week or so I am having problems when making calls, after about 5 minutes calls are disconnected. this happen with every call I make. People cannot phone me, they get my voice mail. When I phoned Customer Care, I was disconnected while I was trying to explain my problem and that they should check all call barring and converting. The lady did not even try to call me back. Can I please cancel my contract with Cell C, I think with all the problems I had with you, it is a breach of contract. I think I must cancel my debit order and stop paying, because one should not pay for services not received. All of this happen with 80% signals. Cell C is inviting more users on their network while they cannot handle the current ones.