Contract cancellation method would have been detailed in the email you received when the contract began. Essentially, you need to email infoservice@magix.net with full details of your contract and ask that it be cancelled. Do be aware that cancellation will take place some days after the date on which your email is received (I believe it can be up to 28 days later that cancellation takes effect) so you may well have to make at least one further payment before the contract ceases.