Changes to Flight Ease airline booking after final payment

[TAD2005]

We have a cruise in October from Venice to Fort Lauderdale. We purchased our one-way Florida to Venice air flight with HAL, through our TA. We got an excellent rate for premium economy.

We have made our final payment for the cruise and the air connection back at the end of July. We have decided to treat ourselves to business class air for the long trans-Atlantic flight. I made this request to my TA and HAL has said to our TA that any changes after final payment must be done by the TA directly with the airline. HAL did the original reservation. Why can't they inquire about upgrading to business class ? My TA is having difficulty even reaching the airline due to hurricane related problems. I checked myself on the airline's website for the paid upgrade, and they cannot help me. They refer me to the travel agent who did the original reservation.

Has anyone attempted a class change like this after final payment, when, I assume the tickets have been paid for by HAL to the airline ?