A little more information (excluding license/subscription number or personal information) would be helpful.
e.g. product you are being billed for, by whom billed, etc. ?
It sounds like you haven't cancelled your auto renewal payment mandate.
Cancelling automatic renewal of the Avast subscription - See
https://support.avast.com/en-en/article/35.
If the funds have been taken:
Refund request -
https://support.avast.com/en-ww/contact/sales_refund If you haven't got the Order ID, etc enter 00000000 and give as much information that you can to help identify it.
