Typically a company owes you money when you leave, like the started part of the month, pending holidays, and the annual bonus/extra pay that you already earned.

If you don't respect your notice period they'll remove your salary over the missed time from that final payment. So in that case they'd remove 3-month salary. Sometimes it goes into the negative, and some companies actually send a bill, but there's basically no consequence for ignoring it. Usually companies don't push the matter.