You are ~1.5 years into your fixed term. AIB will compare your existing rate (3.75%) to their current 3 & 4 year rates (4.55 & 4.6%). This means there should be no ERC for you...but always to get it confirmed.
I don't think the €5k limit really matters here. Pay it off now if you have the cash available.
Your next steps should be:
1. Request the ERC for the full balance of your mortgage
2. Complete the mortgage amendment form (link below)
3. Once confirmation of the break fee is received, sign, scan and send the form to AIB
This will start a new 5 year term at 3.2%