You can change your MAC address by contacting your ISP. I believe they do it free first few times then there is a charge, usually. Might even be able to change them yourself if you change the config file, but I don't recommend that.
Anyway, outright banning the account is fine, why would you want more. Sure, they could upgrade again, more money... who cares. Takes two seconds out of your busy lives you ban someone again.