Rewards 660 Indigo Mastercard Stolen card, still owe anyway Internet

I obtained a prepaid credit card from Rewards 660 in hopes of building credit. I loaded 300 dollars onto this card. I possibly spent about 100. I did make a few payments and then Rewards 660 sold out to Indigo Mastercard. This was around 5 years ago or so. 
Shortly before Rewards sold to MetaBank (Indigo) my card had been stolen. I do not know who by (The Creditors actually keep asking who.. if I knew WHO then they would be in jail). However I did call the Rewards 660 and filed the report with them to have the card cancelled because it was stolen. About 3 months went by and I received a call from Metabank stating there was a balance. Again I explained what happened but they told me they could not pull up the account. After talking to them I was frustrated because my card had been stolen and I did everything Rewards had told me to do. I talked to a bunch of people at that time and thought the matter had been resolved. 

To my dismay I received another call yesterday from the creditors for Indigo. I called them back, explained what had happened and asked for contact information or anything because I CONTEST this bill.. and have been contesting it since the very first call. The creditor said I was "Willfully not paying this bill" I then explained this entire situation again... this creditor became nasty. I told him I never said I would not pay the portion I was responsible for; however, the card was stolen and it was supposed to be cancelled and I explained how I called Rewards, and then when I spoke with Indigo they keep saying they cannot obtain any account information (they can obtain the bill information obviously but nothing else) and they cannot go back... 

I cannot get a hold of anyone besides the bill collector on this account. When I do I am being strong-armed into paying a bill that I have disputed part of since before Indigo had taken over.