Poor customer service

We moved house early January this year and decided to go with Tesco for our broadband and calls because it seemed like a good deal and we have been loyal customers for years. BIG MISTAKE.
We contacted Tesco some weeks before the moving date so that we would be all set up when we moved which was important as we need it for work. Tesco said they would just check that the line was fine but then told us we would have to wait 3 weeks after moving for an engineer to come out. This made life very difficult but we decided to go with it, having already signed up. The engineer came and said there was nothing wrong with our line and so we need not have waited! It gets worse. The broadband service is terrible. It freezes up when trying to use I-player, sometimes for so long we give up. It constantly drops out when using computers and as for using Viber to talk to anyone overseas, it's useless. If I'm not within sight of the router it doesn't work at all.
We have called Tesco about this now so many times. They did post us a new router but that made no difference and when we talk to them they seem to have not got a clue and keep repeating the same questions that we've answered on all the other occasions, promising us an engineer will call back and or come out to resolve it but things are still the same.
Bottom line is, no one is interested, the service is unprofessional and hopeless and we are stuck with a contract for a rubbish service. At our wits end!