if my employment agreement has an arbitration clause in it how do I go about filing a claim to receive the severance and benefits owed me per the contract?

My employment agreement states, "in the event of a termination of this Agreement without cause, employee shall be entitled to eight (8) weeks of severance compensation at a typical historical rate." My position was eliminated on 2/23 and I have yet to receive my severance. They deposited some funds in my checking account but it doesn't appear to be enough and they haven't sent me a check stub to see how they arrived at that amount. I worked 11 mos. at 40 hrs a week and then they dropped my hours to 16 before letting me go. What does "typical historical rate" mean when stating that is what my severance will be?
Since the agreement states "that any unresolved dispute shall be settled exclusively by arbitration"how do I go about filing a claim?