From Purchasing details in the Online Shop regarding the monthly subscription:
"Subscription and cancellation conditions: VEGAS Pro 365 will be available immediately after payment and activation. The charge for the minimum term is payable as a single sum upon conclusion of the contract. The minimum term begins on the date of purchase. The contractual period of VEGAS Pro 365 will be automatically extended by one month at a time until you cancel the agreement. You will be informed well in advance if the extension rate or taxes included change. A cancellation is possible up to 1 day before the end of the contract period. To cancel the contract, please send an email stating your customer number to: infoservice@magix.net"
(Use whatever number you have to help identify your contract.)