Louis, I think your anger at Spectrum has clouded your view of your T-Mobile situation. I also think you may have had some misunderstandings of your plan, which have only come to light on this first time you've hit your limits.
First, T-Mobile aren't "Sneaky a-holes" for having two independent caps for tethering and phone high-speed data allowances. This is a *feature* that many people look for in a plan, as it gives you a degree of protection from service impacts from one usage spilling over into the other.
For example, I used to tether my laptop to my phone when traveling for work. I had a few times where my tethering data usage would spike significantly - Windows downloading a big update, large project files synchronizing, etc., sometimes triggered by a network administrator without me ever being aware of it, or having the ability to stop it. But by having independent caps, I didn't have to worry about these kinds of situations causing any negative effects for my phone usage. At worst, the tethering side would slow down, but my normal phone usage would remain completely unaffected. That's a far better outcome than a single cap, with any overage taking down BOTH sides.
Second, T-Mobile isn't ripping you off for 20 days of service. You might be thinking of your contract as an access plan, like cable TV or a gym membership - sign up for 30 days, get 30 days of access to use whenever and however you wish. But for cellular data usage, you're instead paying for a monthly allowance - a set amount of consumable data. In your case, you had already used up your full 30-day allowance in those 20 days, so there would be nothing left to prorate. Changing your plan gives you a new fresh allowance, so of course you would have to pay for that as well.
It's sort of like going to a restaurant and ordering a cheeseburger, then after eating that burger entirely, deciding you were hungry enough that you should have bought a double instead. You could go back to the counter and order that double, but there would be no credit given for the single burger you already ate, nor for any portion of the larger burger you couldn't finish before leaving the restaurant.
Overages like this used to cost people thousands, sometimes tens of thousands of dollars. I know you're upset, but those T-Mobile policies you're angry at probably worked in your favor this time.
