ISP cancellation

I have an issue with my ISP that hasn't been resolved for over 3 weeks now.
ISPs are not guaranteeing a faultless service, but then you would expect
them do fix problems and report feedback within reasonable time. I am unable
to access my allocated webspace and the ISP support has acknowledged this and
say that they have "escalated the problem to the fault department". Further
communication by email and phone has resulted in nothing, not even a promise
to chase up the matter, only: "Yes, I can see it's in the queue".

This is clearly very frustrating, especially since there appear to be no
light at the end of the tunnel. Unfortunately they have a cancellation charge
of £70. If I drop out, they will probably just take it off my credit card.
How can I prevent this?
.