Dollar General complaint: Retirn

My sister bought me portable heater in Arlington Tx. and it did not work well, I took it with the receiptt to a store here in Mineola, Tx. The manager explained they don’t take back heaters if they’ve been opened, I asked how do you know if they work if you don’t open them? She said I could exchange it for another one and said I great. She said they did not have any and I asked when will you get one. She said she wasn’t. I asked if I could exchanged it with other items and she said no. I would like know is this really your policy when I bring it back and you don’t have an even exchange product not to honor with other items? I wasn’t trying to do anything wrong but I felt like she thought I, I would have been to receive another one but that option was available to do. I think I should have been able to get other merchandise with the total amount i spent on the heater.