I think people ITT are being weirdly bootlicking about the whole thing, and you're in the right entirely. I guess if I were in the same situation, I'd request footage from anyone else in the neighbourhood, or see if the neighbours can make the same call you did to track down exactly who visited them.
People don't seem to appreciate that regardless of how reasonable your bandwidth usage is, a company does not have the right to physically disconnect your house from the internet on your property without warning. In theory, they can legally disconnect your house from their service remotely, but without warning (or maybe they do, but that would have to be in the fine print) and that would also be a major problem. They'd have to assume liability for any consequences occurred by intentionally disrupting your connection.
People don't seem to appreciate that regardless of how reasonable your bandwidth usage is, a company does not have the right to physically disconnect your house from the internet on your property without warning. In theory, they can legally disconnect your house from their service remotely, but without warning (or maybe they do, but that would have to be in the fine print) and that would also be a major problem. They'd have to assume liability for any consequences occurred by intentionally disrupting your connection.