If you aren't feeding live bloodworms then what you're seeing unfortunately is camallanus worms. Make sure to turn off the lights when dosing levamisole as its affected by light. Also, an extremely large water change and thorough cleaning of gravel/fitlers to remove the worms/eggs is essential as fish will get re-infested. If I am not mistaken levamisole does not kill the worms but paralyses them and they loose the grip and drop out from the fish. So to break the cycle you need extreme maintenance. It needs an intermediate hosts like inverts to reproduce so I'd stop any live food, or raw food, if you're feeding them. In fact, its said camallanus eggs could be in any frozen foods too.
The fact that your fish are still alive means the treatment is somewhat working but not fully yet if you're seeing that many worms...
Good luck, fingers crossed. Levamisole is normally effective for these.