If you remove the pump and take it apart, you probably find the plastic impeller shaft has broken in multiple places.
Use a #10 Finishing Nail to gently drive the broken bits of the shaft out of the impeller.
Use a long pair of tweezers to remove the bottom piece of the shaft that might be struck in the little rubber boot in the bottom of the pump housing, if you are able to also retrieve the boot do so..
Once you have the broken pieces removed from the impeller, take the the boot and place it on the head of the #10 finishing nail.
Replace the broken shaft by inserting the #10 finishing nail with the boot on it in to the hole where the boot and spindle shaft was prior.
Clean up the mag impeller slide it on to the nail, I cut two small pieces of cardboard to cushion the placement of the impeller in to the pump housing because of the amount of magnetic pull the impeller has.
Once the impeller is in place, reassemble and install the pump.
Should work just fine.
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