Charged sales tax when removing deceased person from title

I purchased a vehicle with my grandma on the title. It was listed as “my name & grandmas name, last name” on the title.

My grandma passed away. I refinanced my car (for a lower interest rate) and used my signature and her death certificate. The new bank got the title in from my old bank.

I picked up the title and took it to a notary to remove her name from the title. When I did this, the notary had me pay $900 sales tax for $15,000 that the vehicle was refinanced for.

I called my boyfriend and told him, and he told me this was wrong. (He does title work for off road vehicles for 15 years). He said that because we were simply removing a name, the sales tax did not need to be repaid.

I went back to the notary and tried to tell them this. They would not refund me the $900 paid in sales tax. I called 3 notaries, my bank, and spoke with the PA Association of Notaries. They all confirmed that the sales tax did NOT need to be repaid, due to there being no sale, gift, or anything of the vehicle. It was simply removing a name due to death. I am on the original and current loan and always have been.

Was I indeed incorrectly charged? What should I do next?