They’re assholes. They did the same to me (tried to bill me a full years worth of taxes for a school district I lived in for 4 months, almost 2 years after the fact) and after going back and forth with them several times I thought it was resolved.

A few months later I’m waiting on final approval for a mortgage and I get a letter that they are going to garnish my wages in 14 days if I didn’t pay several hundred dollars. Never been more pissed off in my life to write a check but I was so scared of loosing my mortgage I didn’t have a choice.