Seller Issue

[salsuds]

I had a buyer who purchased an phone from me and at first they claimed I mislabeled it. However then they retracted that and said they were taking their frustration out on me and that there was nothing wrong with my listing. They admitted it was their fault. They said they were going to keep the item. However, now after a few days they want to return the item. Can someone offer me some advice on what to do? My issue is the phone only loses value every day I do not have and cannot resell it. The buyer is taking forever to respond. 

[salsuds]

Now the buyer started a return and is trying to put the blame on me. They are saying the phone is not any good to them because the 3G shutdown. However, I do not understand why it would not work still because the phone supports 2G, 3G, and 4G. I am kind of new to selling and now I really do not want to sell on eBay anymore. I am having a horrible experience. I really need help on what to do from someone experienced. I appreciate your time reading this. Thanks. Have a great day or night!