travelling, hit data limit can't remove speed cap or accelerate scheduled data plan change

I have been a Cingular/ ATT wireless customer for decades. I am travelling cross country on AMTRAK. We hit the data limit on our 25GB data plan. I had already upgraded to a 50 GB plan effective in four days. The website offered to backdate this data plan change, but would not complete the process despite multiple attempts. I called  ATT Customer service, they said the only way to lift the data speed cap is to give up my existing plan. Not for the upgraded plan I have already agreed to, that is "no longer available". No, I must sign up for a much more expensive plan if I want to have functional internet access for the rest of my vacation. We have four cell phones and a couple of iPads. I do not think that there is any technical reason that ATT can not remove the speed cap.As  I am now paying $10/GB for each additional GB of data  I imagined that they would like me to buy as many of these expensive GBs as possible, but ATT insists on crippling my phone's speed. My choice is  1) to be without useful internet for the rest of my vacation or 2) to give up a family data plan that is fine for our needs and pay considerably more each month, forever.

In general I am more likely to respond to the "carrot" than the "stick." This situation seems plainly coercive. ATT is not ourISP, and we do not have Cable Tv, so I guess retaining our $3,000 per year mobile phone business is not worth even a minimal effort.

My Grandfather was a phone man at NY Bell for almost 50 years, my childhood home featured a framed "Telephone Pioneers of America" membership certificate in a place of honor. It is going to be kind of strange to be using another provider.