I was a sales trainer for a large French pharmaceutical company that operates in the US. I was asked to leave the position after two years of employment, but by written, mutual agreement, I was asked to train certain sales employees and finish a project.

I was a sales trainer for a large French pharmaceutical company that operates in the US.
I was asked to leave the position after two years of employment, but by written, mutual agreement, I was asked to train certain sales employees and finish a project. Upon completion, we were to sever amicably. The listed activities and bonus/severance due me for completing them were put into a separation agreement which also included a non-compete clause.
The bonus was due by the end of March 2018 and I only received 1/10 of the amount due.
I have reached out to HR and the CEO of the company (my direct supervisor had left for another position after my departure) and I have received no response.
I clearly have a contract stating what is due me,I just don’t how to proceed without it costing me a lot of money. I had counted on the lump bonus expected to pay for a planned renovation and I now have to take out a loan to complete it. I would not have needed the loan if I had been paid on time and appropriately. Please advise. Thank you