Non existent service

I changed to Momentum late last year but have not been able to contact them since then. My calls go unanswered as well as my emails. I have started insulting them to get a response and had two (weeks apart) calls from them. Now I sold my car and I cannot stop my deductions because noone responds! I have never had to deal with such a useless company. I initially thought that it is due to Covid but clearly they do not care about their clients. I want to see whether I will still pay at the end of this month. Totally unacceptable service