I had a similar issue when i moved from Zürich to Schwyz. I spoke to my Gemeinde and they recommended speaking to the withholding tax official at Kantonal tax office. He agreed that there was money owed from Zürich and said they were really slow at transferring. He put a block on my bill from the Kanton and sent an email to the Gemeinde asking them to do the same.

Can't say for sure if he speaks English or not, so if you don't speak German, it may be worth getting someone to call on your behalf.