Don’t panic! You can sort most things out.
First of all what does it look like? If it is a resin it could be one of two different types; polyester or epoxy. Polyester resin (like car body filler) will probably chip off as polyester resin does not make a very good glue, try getting a sharp chisel blade under an edge and lever it away from the surface (wear eye protection). If it lifts off cleanly you are in luck and it’s just a case of chasing the separation down the hull. But if it does not (and I suspect you will have tried that before posting), it could be epoxy resin with a filler powder; this is a bit more serious as that is a good glue and if the guy who stuck it there did a good job he will have keyed the hull so it will have a good grip.
Assuming the old keel bands were fairly straight, ask yourself if the resin has to go, as it will provide a base for your new bands, you could bed them down onto it using Sikaflex 291.
If you are dead set on removing it, and as the keel and bilge keels stand proud of the hull, your best bet might be to take a coarse file to the resin, keeping the file flat and parallel to the surface. Invest in a carding brush to clear the resin from the file teeth occasionally.
The current material of choice is aluminium and Pinell & Bax or Sailboats.co.uk have it both drilled and undrilled in their catalogues. There is a plastic alternative available that glues on, this might be an option. Get some Sikaflex to bed them on , do not use silicone sealant, that’s only good for bathrooms and make sure some sealant gets into the screw holes.
Post some images and let us know how you got on.