Since I don’t work for Avast, I can’t answer that question. I’ve used their free version since 2003 and have never seen this happen.
If you’ve never used the paid product, you also would never have supplied them with your credit card. There isn’t any way for them to charge your card unless you gave it to them. Contact Avast to request a refund https://support.avast.com/support/tickets/new?form=2