Exceptionally poor service

I have an endless and ongoing problem with Supersonc. Battle to get hold of them. Their e-mails return as "unattendet mailbox, Whatsapp no under construction for the past 6 months. And if you lucky enough to get through to a consultant, they promise to call back, and never do. My isuue is I pay for 30Meg up and down. I receive maybe 3 if I am lucky on a good day. Hovever they take my monthly installment religiously withou fail. no-one gets back to you.