I am an independent contractor with a contract stating that I will be paid on the 15th of every month for the previous months earned commissions. I have never been paid the correct amount or on time for any month. I am desperate to get all money owed to me which goes to the end of the year and to get out of my contract. Desperate for answers!

What does your contract say about default?

Are you billing them each month for the services you provide? If not why? Have you sent them a bill for all the amounts owed and not paid? Have you talked to the people who pay, "accounts payable" and asked why you were not paid correctly?

The contract may allow you to sue, or require you to use a mediation group. So you need to read your contract for options

The contract says that "commissions are dispersed on the 15th of every month for all commissions received by the agency in the previous month. Commissions are considered earned by the Independent Contractor once the clients have returned. If the relationship of the parties ends prior to such, no commissions are considered cerned on said bookings by the Independent Contractor". Exceptions as agreed by both parties. Contract may be canceled in writing by either party"
Every single month since this contract has been in effect they have never paid on the 15th and have not paid the previous month's commission. They just pay whatever, whenever they feel like it. I want out but want my money.

So what does your contract say about default?

Sounds like you will have to sue.