severance pay upon dismissal

I worked for 10 years in the municipality. Now I have been dismissed. For 6 years I received my salary by checks. Attached to the check was a confirmation (like a payslip) regarding the paid money. This confirmation always had the letterhead of this municipality. And for 4 years, money was transferred to my account and I was given a regular payslip. Does the method of salary payment affect the calculation of severance pay upon dismissal? The municipality claims that I only worked for 4 years, and those confirmations are not payslips. Is it possible to prove that I am entitled to severance pay for 10 years?