Oxygen Plus Medical review: o2 concentrator I never recv'd, then no return call, still had to pay Affirm, Run from Both

Description Purchased an oxygen concentrator online and was sent the wrong item. Called to inform the company and ask for an exchange or refund. Merchant stated that they were out of the model I requested and would not have one available for 2 weeks. I asked for an RMI for return and was refused that courtesy so I returned the item with a tracking number and called to let the company know i had done so and to expect the item within a couple of days so that I did not fall outside of some limit of return. The merchant refused to accept the return and returned to sender. I never received the item and have no idea where the item is, so I contacted Affirm the finance company to let them know the issues I had been having. I did not want to be held liable to pay for an incorrectly shipped item or an item I do not have possession of. Affirm did not want to get involved with merchant's failures but did initiate a dispute. When the merchant states that is not their policy to accept returns without an RMI., the dispute was closed. I am now being help responsible for paying for the item. Have been referred back to the merchant that refuses to return any correspondence and don't feel they are obligated to refund or exchange the item. Upon ding research and inquiring to other oxugen concentrator companies, i learned that the transaction was illegal because oxygen concentrators are considered medical devises that require a prescription before a legal sale can be made. I contacted the merchant with this information and they refuse to rely at all. I am asking for assistance with this disreputable merchant to help facilitate a full refund. I have had to secure an oxygen concentrator from a more reputable merchant and this time I did receive the correct item and very promptly and without any complications. They made sure that i got what i ordered and was happy with my purchase.