forum ban?

[Thehotpots]

a forum banned me for making two accounts, only I didn't make two accounts. my sister and I each made an account and we live together.
are IP addresses the reason why they thought we were the same person? if i get a new addresses can i get around the ban? does using a VPN fix that? if not, what would be a way to get around the ban?
if this is a really stupid question and doesn't make sense, im sorry! this really isn't my area of expertise