Carnival/Barclay Reward points redemption rip off, nightmare! Internet

I currently have 45,000 fun points.  I received the email with the redemption information.  It states that for airfare I can redeem $150 for every 20,000 points and $37.50 for 5,000 points.  So I call to confirm that if I make an airfare purchase, I will be able to apply the $337.50 (from the 45,000 fun points balance) towards the purchase.  I was told that yes, I would be able to do that and would simply have to logon to my account to do so after making the purchase.

So I went ahead and purchased airline tickets.  I logon today to apply the $337.50 credit to my purchase.  It tells me, sorry, you do not have enough points to apply for this purchase (the purchase was for $367).  I contact customer serviceand speak to five different people.  I was left on hold, I was transferred back and forth from one department to the other, I was read the same exact script from each and every individual.  Finally I got one person on the line who told me that I couldnt apply a partial credit to my purchase.  That in order to apply the points to this purchase, I would need to have enough to cover the entire $367.  Theres only a $30 difference here!  They tell me that I would need 49,000 points to cover that purchase.  So I would need 4,000 more points to cover $30??!! 

I ask to speak to a supervisor (Jason) who apologizes for the inconvenience but reiterates that theres nothing they can do and partial credits can only be applied to carnival cruise purchases.  Not to airfare.  So I ask to speak to someone else who can assist me better than he can.  And he tells me that if I want to speak to someone else then I need to hang up, call again, and ask for another supervisor.  I said NO, I will not hang up and call again because I have already been at this for an hour and this is unacceptable and ridiculous.  This was not explained  correctly when I called to confirm and after spending $45,000 on this card, I dont think you should be giving me a hard time about crediting $330 on the account!  He repeats that theres nothing else he can do for me and if I want to write to the correspondence department about this, then to go ahead and do so.  He proceeds to give me the mailing address and then HANGS UP ON ME! 

Im so angry that I think Im literally fuming.  I feel like Ive been so ripped off.  The only reason I made this purchase on the card was to apply the credit.  Is there anyone else who can help me?  What should I do?  I feel like all of this information is not presented correctly to the customer!