Allowing for some roundings, it looks like someone divided the holidays into 12 monthly segments instead of by 13.
The proper way to handle this is hands up with good communication, not just hiding behind a payslip hoping no one notices. Maybe give 1 year notice that it will revert to correct system as per contract.
I've said it a few times on this site, the level of ineptitude in many payroll departments is staggering. Very often, run by people who came in as a junior admin or secretary and moved into payroll with no proper training.
I'm sure too, some employees knew about the error all along...