Read my comment above in response to this. Airlines have to pay out for baggage service every day for bags that they never had possession of. It's how the industry works. Avianca boarding the OP was implicit acknowledgment that Avianca is agreeing to take responsibility for getting the OP's baggage to his or her final destination, too. If Avianca doesn't want that, then Avianca shouldn't have boarded the OP on their flight.