Stuck in a contract I said I didn't want

My wife is trying to cancel her services for her tablet because she is moving to Scotland in September. They said to her that there is a contract on the tablet and it cannot be cancelled without paying the remaining fee. This is unacceptable because the Tablet was fully paid up and the topup account simply gets airtime every month. When they phoned me and asked to do this conversion from a contract to monthly prepaid several months ago, I mentioned explicitly that I did not want to pay cancellation fees (i.e. wanted to be able to cancel at any time) and they accepted. So the fact that there is now a contract on the account is a mistake and must be corrected. I refuse to pay the cancellation fees on this. I cannot call the cancellation department from abroad to discuss because the number doesn't work from here... for queries please phone me on my UK number I have given you. Please turn this complaint into a compliment by doing the right thing and fixing this quickly.