Question

Hello and blessings!
A deceased relative of mine purchased a seat in a synagogue for about 3,000 shekels. He passed away before he had a chance to benefit from the seat, because it was a relatively new synagogue and the seating was still in flux.
After his death, his wife approached the synagogue trustees to understand what would happen with the money for the seat. They replied that the price of the seat had gone up significantly, and that in order to receive a seat (for one of her children or sons-in-law to sit on), she would have to add more money. They made the same demand for an additional payment from all the other worshippers who had purchased a seat as well. (Some refused to add more, and the synagogue reached a compromise with them: a smaller additional payment in exchange for a seat.) She does not have the money to add, and therefore when the seats arrived she did not receive a seat. She wants the money back so that she can donate it in her husband’s memory, but the synagogue claims that the money was a donation and does not belong to her. (According to them, the seat was only a gesture of appreciation from the synagogue for the donation.) As a goodwill gesture, they are willing for her to add money and they will donate cabinets or something else in his memory.
Are they obligated to give her a seat?
Do they need to return the money to her?