In this field, it is incredibly rare not to have such an agreement in place for reseach scientist such as yourself.
Before we get to the point of litigation, which may be necessary, ask them to provide you with any and all IP generation contracts, agreements, policies and procedures that they have at their disposal relative to your work.
There should be something in there that at least pays you royalties on the sale or commercialization of your patents. It would be very unusual if they don't. If they don't you may have a case for fraud here against them.
Understand that typically the entity that employees the inventor and provides resources for research will be the entity that has the primary rights unless a contract is negotiated to the contrary. That said, you should have some rights here and certainly should be in line for more money than you have received.
Let me know if you have any other questions or comments.
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Best wishes going forward!