As soon as I know, Dreambox DM8000 can be used with dual-login to watch 1 and record the other one channel, as MgCamd is sharing your requests from receiver to the server between 2 channels at a time.
So, if you think, that you need no dual-login, OK. To cancel you current subscription, you need to send e-mail to the Moderator, then disable dual option via the billing, otherwise you will always be charged for dual-login.
regards