I agree with Oysterman.
Leaving aside the AVC issue, the OP got 2,600 of this year's (and next year's) pay in advance, and was only taxed at 20% on it, rather than 41%. So they have got €546 more than they would have if the boo-boo hadn't been made.
Taking this into account when you look at the AVC, they only received relief at 20% rather than 41% they'd have obtained if if they paid it this year, so they have lost out on €168 of tax relief there.
So between the jigs and the reels, taking last year, this year and the first 6 months of next year together, the OP's net pay is €378 higher than it would be if the mistake hadn't been made.
That doesn't mean it's not a pain in the This post will be deleted if not edited to remove bad language for you OP, as you are now down €80 a month til next year, but I'm just saying, the numbers do actually stack up slightly in your favour...