Xfinity mobile agent at store forgot to cancel my iPad line and I got charged for another month at ATT

I just got billed $80 by ATT because they Xfinity agent at the store forgot to cancel my iPad line as he was transferring my service.  I spent over an hour at the store and we went through passwords and numbers and everything and then he forgets to kill the iPad line.  

I called ATT and they said that this happens all of the time and the bill is my responsibility and they would not give me a credit.  They did cancel the line.  I'm probably going to get another bill as well.

I called Xfinity customer service and they told me to call ATT and beg for a refund.  Nope, ATT said this is my responsibility.

So Xfinity screwed up and I'm left with an $80+ bill.

BTW, this is on top of a $100 charge I got because hidden in the fine print under the fine print is that international data roaming is not available for the iPad and we used our iPad in Canada on our last trip.

So I am pretty pissed off about changing so (as Senior Citizens) we could save $100 a month but now I'm out $100 for this roaming thing and $80+ because the Xfinity agent forgot to cancel my iPad line.

What gives?

Is there going to be another bill out of nowhere hitting me next month?

As for the cellular service itself, it's been OK.  Definitely not as good as ATT - its like there is a few seconds pause added to every data transfer, especially when initiating video or music.

Also we are getting "you have too many video streams running" message when we are just watching one video on the iPad and nothing else.  So not sure what that is.  

Very disappointed so far 2 months into Xfinity Mobile.

Will also send this direct to an agent but wanted the community to know that Xfinity mobile must do better!

Cheers, Joe