Hello Rustam
You are talking about the GA Travel Card, Generalabonnement in German.
The yearly GA subscription has a minimum contract duration of 6 months and cannot be terminated earlier, unless in case of death or health issues that make travelling impossible (attestation from a physician required). And this no matter if you pay it yearly or monthly.
If you are unsure how long you will need the GA, the 1-month GA Travel Card is the abonnement of your choice.
Kind regards,
Roland