I don't know where you are flying from and to but Colombia has a provision for tickets sold in Colombia whereby airlines are allowed to charge a non-refundable administrative fee included in their tickets.

It's Artículo 3 de la Resolución 3596 de 2006 de la Aeronáutica Civil

The resolution is somewhat badly written and wilfully misinterpreted by LAN and Avianca. So even when you should foreseeably be refunded 100% of what you paid, normally when an airline cancels your flight or in your case when you have a fully refundable ticket. The airlines see the resolution as an obligation to charge you this fee and never give it back to you.

If Avianca is referring to this when they say they will not refund 100% of your charges and fees then look for the tarifa administrativa in your fare breakdown.