So yeah i have a booster ( 50 ) since like a half year nao ( idk ) and i dont want it anymore, how can i abort the abo?

To cancel your subscription for the recurring booster you must go to paypal, click the 'History' link under the 'My Account' tab.

Then 'More Filters', 'Subscriptions and Agreements' and click Subscriptions. You should be able to find it there and cancel it.

Do you get a refund if you cancel the subscription?

No, I do not think you will get refunded it just cancels anymore payments.

Edit: For ongoing subscriptions which I think he is talking about it will cancel any further payments for the booster.