The stamp duty year runs from April-March, and is paid in arrears.
The duty is applied once per year in April, or on closure of an account. Provided you only have one card at a time, you shouldn't have to pay twice.
In April 2014 you were charged €30 for the 2013/14 year.
When you closed your AIB card, you should have been charged €30 for the 2014/15 year (it might have been included in the balance you transferred).
You shouldn't be charged for the 2014/15 year again (which would fall due next April). What normally happens is that AIB send you a document to confirm that the duty has been paid for the 2014/15 year, and that's what you send to PTSB. Be sure to keep a copy of the document.