Grandfathered Simple Choice

I'm having the same problem with grandfathered plans of 4 lines for $100 here. I reduced to 3 lines several years back and my bill remained the same 3 lines for $100. Sadly, TMobile treats new customers better than 20+ year, loyal customer. The fact they merged with sprint and reduced competition in the cell phone market doesn't help. Now, $100 for 4 lines is only available on prepaid plans or holiday promotion like this for new customers.  

https://www.t-mobile.com/news/offers/t-mobile-holiday-offer-4-iphone-15s-and-4-lines-for-100-mo