Tmobile Constant excessive overcharging Nationwide

I have been with t-mobile for 14 years noe and they have charged me off and in for stuff and would take months to straighten out. They recently cancelled my tablet service that I had been paying $8.50 for up until last November. In November they increased the charge to over $38 per month it has been a constant battle to get it straightened out. This month they charged me .ore than $94 for a one phone plan with 2 g of data..the bill should have been around $60.00....I am so sick of calling there customer service department. For the past year I have been unable to use my tablet and yet they continued to charge me for it. I want the $8.50 for the tablet free for the past 12 months refunded to me and the over charges they are putting on my bill. This company is an abusive nightmare and should be put out of business.