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, MalwareBytes Premium--HP Envy Win10x64, MalwareBytes Premium,--Both systems Avast Free v2015.10.3.2225, MalwareBytes Anti-Exploit Free, Super Anti-Spyware, Spyware Blaster, MCShield, Unchecky, Firefox (latest build) and, various browser security tools.
"Look before you leap!" Use online scanners before you click on any link.