How reliable are information or solutions promised by support agents (chat)?

I have reached out to live chat agents (Human) for my problem with the router (wifi). They tricked me into sign-up for xfi complete, which have 5 USD extra charge, and promised to provide me an XB8(with wifi 6e) router and my problem will be gone. I was asked to collect it from the store. I visited the store just to be greeted by some rude dude, who asked either take the used XB7 router or get it from the live agent When I tried to show them the chat transcript. 

I took the XB7 router, in the hope it would work .. but it didn't work.. on top of that ... all the the devices from a previous owner is now added to my account with all physical address, and some metadata of the owner. Then I contacted support multiple times to report the problem and complain i got used XB7 when i was promised for XB8. Then i discovered that extra charge USD5 was for unlimited data not for the devices. I have monthly uses of 350GB only, I check it regularly, which is 4 times less than cap. (1.2k GB). When i asked to discontinue that services and adjust the bills. The live agent said it is being adjusted and enrollment was reversed, but today I got charged for full amount. 

Just recently(less than week ago), I got another router shipped to me, which was supposed to be new and won't have a problem. again it is having the same problem. when i split the wifi, 5Ghz wifi just disappear after few hours .. and none of my devices (mac, windows, android, linux) can connect.