replacement of Telkom landline system by wifi system

without my consent my fixed line telkom telephone service was replaced with a new telephone system which works through wifi. The sales lady said that the copper lines were going to be abolished as from 2021. So when the replacement phone just arrived I left it. although I had not placed the order yet. Unfortunately the system does not work properly and I seldom manage to answer incoming calls. Apart from that, the sound quality is so poor that it is practically impossible to have a conversation with anyone. There is a loud hiss of interference and at times it is like sitting under water. Sounds weird but I have no other way of describing it. I have tried to log calls but there is no reaction. Once it was suggested that I get a new phone. I am sure that is not the problem. It is brand new. Easy way out kind of suggestions.