How do you contact T-mobile's complaint department? Is this it? How do I email or write the CEO?

Back a few years ago (we've been with them 7 years) the Customer Service was amazing.  Now their "experts" either don't know what they're talking about, or get paid to lie.  I don't know.  A little over two years ago, they added a line at my request (I called three times, and all three "experts" said we could do that, so we did), and they said we could get a new smartphone at half-price, so we did.  Well, for a few months, it was half-price.  Then they told us that our plan didn't allow for the addition of a third line.  I had to switch that line back to the previous carrier.  And they added a charge for the few months of paying half-price monthly installments for the new phone, then started to charge full price each month.

Has anyone else had this experience with T-Mobile?  They need to be called to account.  I talked to another "expert" about a month ago, and they said they could switch the line now.  I called the other carrier while still on another line with T-Mobile (a recorded line, because- you know).  They gave me the port-in code.  T-Mobile ported the number (again).  Then the "expert" told me that nope, we'd have to pay almost double for the monthly service.  I ported it back while still on the phone with him.  Then I spoke to his supervisor about the previous ripoff with the "half-price" phone.  They said they'd file a request to get me half my money back.  It takes up to a couple weeks, they said.  It's been over a month- I have heard nothing.  My last call with an "expert" took over two hours, by the way.  We have a corporate store nearby.  One of the nice employees there used to work in corporate CS as an "expert".  She told me that our monthly plan includes Netflix.  I disagreed, but she reassured me.  I checked. I know now that even when the "experts" move on to other positions, they're still always wrong.  How does T-Mobile not know this?  They host this forum. They need to be held accountable.