The my(dot)avast(dot)com is completely separate from the billing department.
If nothing else you have the option of contacting you credit/debit card provider
and put a "stop" on the payment.
Dell Inspiron, Win10x64--HP Envy Win10x64--Both systems Avast Free v2016.11.1.2245, Comodo Firewall v8.2 w/D+, MalwareBytes Anti-Malware Premium, MalwareBytes Anti-Exploit Premium, Super Anti-Spyware, Spyware Blaster, MCShield, Unchecky, Firefox (latest build), Chrome (latest build) and, various browser security tools.
"Look before you leap!" Use online scanners before you click on any link.