A little back story. I was part time at my job working 25 (instead of 37.5) hours a week for a few months. Our pay roll had changed during this time to twice and month instead of bi-weekly. I made enough as part time that I never needed to look at my statement. However, when pay roll changed they started paying me a full time salary despite me working only part time still. After 3 pay periods of this, I went back to full time. I've now been working full time for about 3 months and just found out about this over payment.
The catch is, I've put in my 3 weeks notice to go back to school. Now they're saying I have to pay back $3000, which I don't really have to give back in one chunk like this.
My question is: Is this legal? Can they do this? If it's their mistake, am I actually forced to pay it back? Payroll has made this mistake before when I first went to part time, and I gladly paid back the money they over paid because it wasn't a problem then. It is now.
I live in Ontario Canada. If there's any information you need, please let me know. I must admit I'm a little flustered writing this question.
EDIT: What if you don't have the money? I've given my 3 weeks to go back to school, not start another job where I can actually get the money to pay them back.