Billing issues every month and promotion at time of signup not honored

I have been a customer of Tmobile since June 2013 and have my account in good standing. I have 12 active lines on my account.

In September-October (when my account had 9 lines) I encouraged my family members to move from Verizon to Tmobile and convinced them with the great deals on mobile phones. At the time of porting/moving their account from Verizon, I was promised deals on 3 phones 

Since then, I have been on calls with Tmobile customer service for hours every month and each one of them keep telling me one nonsense after another. They keep pushing the blame from one person to another and keep promising me that my problem will be resolved in the next billing cycle. And every billing cycle I have to call them yet again and spend yet another hour listening to listen to yet another false promise. Until now when they point blank told me there is nothing they can do and I should reach out to customer relations. The supervisor even refused to speak to me. 

This feels like extremely bad service and I am beyond frustrated and disappointed. 

The issue is that my bill every month should be $50 less than it is from the device promotions! That is $1200 over a 2 year period which is a significant amount in the economy and inflation period. The one-off credits they keep applying to correct their mistakes are not sustainable and not enough to offset the hours I have wasted talking to customer service and all the money I'll lose with the discounts failing to apply.