Returned phones not received

[vcarpenter33]

I transferred from Sprint to Verizon in August and was told I would get a credit for each phone toward a new phone upon their return. I returned 3 phones but have not gotten the credit for them. I have spent hours trying to get this resolved. I spoke to someone weeks ago that said they had received the phones and that 2 had processed and they were waiting for the last one to process. Now they are saying they have no record of the phones arriving. I kept the UPS receipt until I spoke with the representative that told they had arrived. I no longer have it and now I have a serious problem. I do not know what to do. UPS says that because it was a preprinted label, they cannot look it up. Is there any way to track the label from the store on the day I purchased the phones?