As long as the CC account is open you are liable for the SD. Close it if you don't need it or don't want to pay the SD. Too late to avoid it this year since the tax year for CC SD purposes starts on April 2nd.
I had the account suspended so I could just concentrate on clearing the balance and not use it but still have the option of re-activating at some point in the future once the balance was cleared.
If the card doesn't work because the account has been suspended, then it's not a payment instrument so I think the OP should be exempt from the stamp duty (but I'm not a lawyer/tax expert!). He should ask Revenue to clarify perhaps.