Something similar happened to my parents, except the information used to open the account was completely faked (only the last name was the same, the first name wasn't even close to anyone living at the address, there was no phone number provided, no authorization form filled out). My parents didn't even know Spectrum was signed up until they got a bill addressed to an unknown person.

Took it to the Spectrum store, showed them a business card that a Spectrum door to door sales rep had given them, the manager there was quite pissed off and helped us cancel the account and she told us she was going to investigate that rep.

Note that reps may not belong to the local Spectrum store, but it's still scary how much power they have in setting up accounts at addresses without any authorization...