If you have your last payslip meet with your local welfare office and pass that on to them, it should say that it was a final payment on termination of your employment.
Ring the Revenue Commissioners and explain to them that you have not yet received your P45.
If you are in financial hardship, meet with your local welfare officer and explain your situation. Each social welfare office has a fund for situations like this. See if you qualify for family income supplement until your unemployment benefit materialises
HTH