Welcome to the Magix user to user forums. No-one here is a Magix employee so we can only offer basic guidance to you.
You want to cancel your subscription, to which program?
Full details of how to cancel would have been in the email you received when you began your subscription, including the terms under which cancellation can take effect. e.g., you may have to make one further payment before the cancellation occurs, depending on when you notify Magix of your intention to cancel.
If you cannot find that email you need to send an email to firstname.lastname@example.org and give full details of your subscription and ask that they cancel it. Again, there is likely to be a requirement for an additional payment to be made since cancellations often take effect only after 28 days from the date you state that you wish to cancel.