It is lawful to avail benefit from the health insurance which is initiated by the company itself. If your company does not pay the whole charges of the treatment rather it takes 20% from you, then also it is lawful for you to get the rest benefit. When you did not seek health insurance nor did you pay any amount then the benefit that you receive shall be considered as contribution from the company.
Allah knows Best!
Darul Uloom Deoband