Did you book entirely on line? Your TA should have been able to verify the on board credits. Also, I believe there is fine print in the excursion documents that absolve the cruise line of any trouble or failure of the excursion operator. I have encountered that myself. While not very fair, I think it is the norm.
As mentioned before in this forum, please write a letter to the customer service dept. of the cruise line and explain the frustrations and difficulties you encountered. You might get response to the inquiry. I know that I have done this and have been satisfied with the result.