Surprise outstanding condo common expenses

Recently, I received a letter from my condo management company stating that there was a historical unpaid month's common expenses for my unit. I paid the amount, and since the outstanding month pertained to the month immediately before I purchased the unit, I requested my lawyer bill the previous owner for the amount.

The previous owner provided bank statements that strongly suggest they already paid the common expenses for the month in question. After seeing that, I went back and checked the status certificate issued before I purchased the unit, and it stated clearly that there were no outstanding fees before I bought it.

I've asked condo management to explain the discrepancy multiple times, and keep getting the run-around and dismissive answers stating that there was an unpaid amount and that the payment I made wasn't a duplicate.

Now, the previous owner won't reimburse me, the lawyer won't file a title insurance claim, and condo management refuses to admit they double-billed me.

Does anyone have any advice on what I should do? It's only a few hundred dollars but it's very annoying that I'm being ripped off by the condo and it seems impossible for me to be able to prove that there was never an outstanding amount.