Why are we being penailzed for paying with a credit card?

Math is off.  If it's 4% off the max end(which I seen large businesses get 6%, and small businesses get closer to 8%) it's per $100 isn't 5-20 cents.  It's $1-4.  If they are getting in fact charged 6% then they lose $6 per $100.  If they give the $5 discount that's $1 per hundred.  That adds up monthly, and that would be at least 10M loss per month, and 100M per year. Don't forget T-Mobile also pays the taxes on top of that. We know for a fact for a long time T-Mobile profit margins are much lower than AT&T, and Verizon all while they also charge fees which is honestly nothing more than padding their profits margins.

No I do not work for T-Mobile or a shill.  The company I work for depending on region we use all 3 providers which ever gives us the best coverage in those areas.  We often have to go to remote areas and coverage is a must.