Did you buy the Don membership when you still had some time left to run on the Standard one? When you buy a membership it will not kick in until any current one has run its course. You cannot permaturely terminate one membership by buying another.
What does your online account say about your membership status (Standard I presume?), expiry date and calls/texts/data/credit balances?
If your Standard membership still has time to run and you have used up your calls/texts/data and need to use those services then you probably need to buy an add on:
http://48months.ie/deal
If none of the above helps then you may need to log a support request to get 48 to assist you:
http://help.48months.ie/requests/new
Hope this helps.
P.S. probably not a good idea to post your phone number/personal details on an internet forum just in case...
