Are the remaining funds from the insurance due from the questioner to his former company considered a debt upon him, knowing that the company did not deduct them in full, and that it had previously withheld his rights?

You are not required to pay the remaining insurance installments to the company, because insurance in most of its forms is commercial and forbidden. Even if it were cooperative, there is no basis to compel you to it. The company's requirement for its employees to do so is its own affair.