Refuse of return to Suppliers

Last year did buy a item by 1N City Computer Mania @ D-Link Dual Band Wireless AC750 Modem they refused to return to supplier as do not have slip but on box says 07/ 08/ 2017.The item have two year Warranty, I am also a dealer if item are under warranty must be sent to suppliers.If problems with the item pay or refund them. I did get a weak customers help from them & I did normal recruitment people to there shop but think they are not able to help people with new Graphics cards or Modems.