Refund all charges you took unauthorized which includes everyone.
Presumptuous of you. Unethical too.
→ https://www.avast.com/faq.php?article=AVKB24#artTitle (Orders and Renewals)
Monthly ?
That sounds you have a subscription on avast secureline.
If you did not disabled the auto renewal, then yes you will be charged each month because you agreed to it.
Only refund that you (likely) can get is for the last payment if you ask avast for it within 14 days after the payment took place.