Bad service

Im very unhappy with service recieved from cell c i did an upgrade recieved the device wasnt happy so i returned cell c billed me R602 for that and on my statement it shows im billed from 1st till the 31st of december for a device i returned upon calling them today i spoke with 4 different agents and not one of them could assist me send me from pillar to post ,why cant they just be honest and tell the client they not dont know what they talking about as to become passive aggressive ,im still here without any answers and no one could give me clarity on my bill or atleast break it up for me .The one agent told me on wednesday 13th of december i dont need to pay that i can just ignore the statement ,but now his nowhere to be found the one agent says its the bill for the new device i recieved on the 14th of december now im confused cell c is clearly dont know what they doing or im stupid