Switched from verizon to xfinity and was promised a great plan + a military active duty bonus + having old line paid off but lied too.

As the title says I was told on the phone my old verizon plan would be paid off in full and I could migrate to xfinity. As well as not having to pay a bill with xfinity until next year. However I have been receiving a bill for $980 dollars and some cents which is ridiculous, and my xfinity app says my bill is due on the third of January for $30-$60 dollars. I was even told by the debt collection agency in regards to the bill that I tried to dispute, that it would be sent to collections and my credit score would tank. Why would I be promised this if it is not the case?