Xfinity agent CHEATING

I was planning to change the internet plan to unlimited data, and the agent told me I need to get the bundled mobile device for the unlimited data, no extra charge for the mobile. The agent confirmed with me more than 3 times there will be no additional bill, the ONLY ONE internet bill will include the internet AND mobile service. I really do not need an extra mobile phone, but just for the unlimted internet data, I agreed the offer. The phone just lay on the desk collecting dust, and creating a second bill, yes Xfinity started charging me for the mobile device and usage right away after they created it for me.

I contacted them to cancel the mobile service and return the device, the first agent deactived the mobile service, and guided me to return the device to Xfinity Store, but the store did not take it for it's over return window. 

Then I came back to chat, the second agent reactive the account and escalated the issue to their advanced team to create a RME ticket for retur lable, but I need to reach back in 30 minutes for the RME ticket.

After 30 minutes, I reached the third agent for the RME, and the agent told me: return window is over, and transfered my chat to other  agent right away. Issue not solved

All these agents, which one is telling truth and can be trusted?