Intermittent Internet Connection In A Technicolor Tg582n Pro

I was previously with sky and never faced any bother with my wireless broadband. Recently to my regret we moved broadband (amongst other utilities)to Utility Warehouse (UTW) who's broadband is through Telecom Plus. Anyway since joining with them I have had no end of bother with intermittent internet connection. Sometimes we get a stationary green broadband light then after a little while then we get a flashing green broadband light. We are constantly either pin resetting the router or switching it on and off at the rear, where it will work for a small amount of time then connection is lost again. The router that they have given us is a technicolor tg582n Pro. We have had two of these as originally we thought that the router could be faulty but obviously that is not the problem as even the second one is dropping our connection. We bought another filter incase that was the problem and even tried plugging router directly into phone box and still didnt work. Utility Warehouse have been about as much use as a chocolate teapot and we are so <unhappy> that we are paying for a service that does not work? They said that our cordless phones could be interfering with the signal? Is this maybe the case and the phones are running on same channel as router thus causing interference? We had these same phones when we with sky and they never caused interference with our broadband. I was going to try connecting my laptop via ethernet cable to router. Sometimes the landline crackles (since UTW installed a new landline & new tel number) so it could even be that? UTW will not send an enginneer out to check their line. we are at our wits end, about to cancel their broadband and go back to reliable sky.