Your credit rating will only be affected if Halifax records a missed payment with the Irish Credit Bureau. From what you say, the error appears to be theirs so I'd be inclined to get a letter from them confirming that they made the error and that they have not recorded, nor will they be recording a missed payment on your Irish Credit Bureau record.
If it really concerns you, you can also request a copy of your ICB record for a nominal fee in a few months' time.