t mobile bill keeps increasing for no reason

@Prash 12 lines is a lot of lines. Are you keeping track of what they are all doing? Are the accounts locked down so that they can't add stuff, buy phones and accessories or make international calls?  Once you've assured yourself of this, I would generate a form letter that disputes charges on your bill, line by line, and just send T-Mobile a letter each month disputing the bill. The company hates doing business this way. It will probably prompt them to either fix the problem or fire you as a customer.