FBA stock linked to deleted listing and not visible for customers

Our FBA inventory is continuously listed to old SKUs, which are deleted listings. Therefore the FBA stock is not available.

The correct listing (with a different SKU) automatically changes from FBA to FBM when our FBA stock is sold out. Because the FBA stock is listed to an old SKU, our correct listing changes to FBM, because there is no FBA inventory visible.

When we change the correct listing to FBA by hand, the FBA stock is listed again to the correct SKU and visible on Amazon. But after some time the FBA stock is listed again to an old SKU and not visible anymore.

This is kind of a loop.

Does anyone have a solution for this?