Celebrity cruise question?

Hi .We sailed with Royal Carrabean three weeks ago ,and i was ill on the ship for a day ,and i was confined to my stateroom .However Royal Crrabean sent me a certificate of �75 for me and my husband to take off on our next cruise with them .Now i understand that Royal Carrabean and Celebrity are amalgamated .What i would like to find out is can i just go into a r=travel agents and will they take the �150 off the price of the cruise please?