Useless service

I write knowing there will be no response. I ported from FNB and since then I am unable to receive calls from certain networks. When dialing out there can be a delay of up to 1 minute before call starts. They told me 72 hours and will be sorted......well 1 week later and no feedback. With 1 year left on my contract what do I do to get out of this terrible mistake i made of using a pathetic service with 0 customer service. Every time you speak to a different agent they give you a different answer. Clearly no one knows what they are doing ,