no receipt for returned unit

Yesterday I was told by a support technician that I could go to the Evans Xfinity store to exchange my non-4K DVR for one that is 4K capable.  The retail sales consultant took our old DVR and upon giving us the replacement unit said that she could not give us a receipt because her printer was not working.  We were told that a receipt would be emailed to us.  We have not received a receipt.  We do not like not having a receipt for the unit we returned so today we returned and were told that they could not give us a receipt nor email one to us.