I see you mentioned your mortgage went up after the reassessment. I would contact your mortgage company and tell them you received this letter. Since you have a mortgage I would assume they sent something to them to indicate the escrow account had a shortage or what. I would get a copy of each year showing the inscreased amount and see if it matches what they are claiming. Also, I would not ignore the letter and instead ask them for proof of the debt. How they came to that amount etc. it’s possible something got mixed up.