can Fixed Rate be increased in the middle of 3 year term

Hi. Have a 3 year fixed rate mortgage. lets say it was 2%... about half way through the term a letter arrived from mortgage co to say they were increasing to 2.5% . And lo & behold the payments are now up that extra amount.
Can they do this?
Surely if it's fixed - it can't be changed until the end of the 3 year term?

Or is this another great irish case where fixed doesn't really mean fixed.

Have you queried the bank on this? Fixed rate should mean exactly that. Have you checked if there are any clauses in your contract which would allow this?

It's hardly a 3 year fixed with the first year discounted?
What lender is it?