payroll errors

I work for a large company in ireland and my wages have been wrong for the last 3 months in a row. Dec i was short 1200, jan 500 and this month 500..i ring every month and they say its a system error and takes about 8 days to refund..what can i do to ensure this is corrected..also causing hassle with outgoings..with my mortgage coming out of my account i ve been left without money until the refund goes through

You will have to escalate it to the Financial Controller or some other senior person.

Are others affected or it just you?

Had a similar issue last year with my employer. Working with them a number of years, new system implemented and a few of us were effected. After 2 months (pay packets) being incorrect enough was enough. Went to Finance dept and insisted a cheque be written their and then for the amount outstaning plur referral fees for payments being missed from my account. Usual story of can't be done etc so got brazen and knocked on door of Dept Director. Expalined issue, he said it will be sorted and lo behold at midnight two nights later all monies paid to my account.
You need to suck it up and demand money for the work you've done. Money being left short in your wages doesn't affect the wages dept, it affects you and they should be made accountable.
By the way, I still work the same large company, there was never any backlash.