So CS say they've put you on the 1.5meg service (& so will presumably be billing you for the 1.5meg service), yet when checking it yourself, & via Tech Support, you're still on the slower (& cheaper) 750k service?
I guess they're having problems....
Have you managed to get through yet?
Make sure CS understand that you are still on 750k. It's also definitely worth pointing out to them that if you're still on 750k, you should only be paying for 750k.