The worst customer service

I spent over 2.5 hours on the phone with T Mobile earlier today, and this evening I have been on with them again for 330 minutes - and I'm typing this while on hold.  They can't solve my simple problems, I haven't spoken with anyone who has an iPhone, they have lied about having iPhones, they barely speak English, they refuse to transfer to a supervisor, and most importantly they don't even know the features and benefits T Mobile and iPhones offer.  Eventually the person told me that his supervisor was available, but he transferred me to a fast busy signal - so effectively hung up on me.  He obviously knows my mobile number, but isn't calling back.  My voicemail transcription doesn't work on one of my 5 lines - but I've spoken to half a dozen people at T Mobile and no one has ever even heard of this (automatic) feature, and one of them turned on voicemail to text, which is likely going to show up on my next bill b/c it isn't a free feature - and it isn't a feature I want.  Hard to imagine they could be this incompetent, and this unfamiliar with their own products (I purchased this iPhone X (and 14 other iPhones) from T Mobile.  We were also part of the breech and they won't turn the McAfee on for this line - they keep trying to sell me a different form of that service.  The customer service people have no training whatsoever.  It's probably time to switch cell phone carriers.  I've never experienced such poor service - and I pay them thousands of dollars per year for my 6 lines.  Very frustrating.