how to leave a good customer service review?

I have been with T-Mobile since I was a teen in high school. I'm a 33 year old adult now. Transferred my account over from my mom's account when I was able to afford my own bill. Eventually added my girlfriend. Later my son. I did a free promotion for a cellular watch for my son. The watch never really worked properly after a month or 2. It would hold a charge long and didn't want to charge. We made due until it wouldn't charge at all. I called T-Mobile to see if I could replace it but do to use not having insurance on a free watch it was nothing they could do. So I canceled the watches cellular line because we didn't have a device for that line. I was then told I had to pay in full for the free watch. And the full amount due was higher then the watch was currently being sold by T-Mobile. The same free watch that I already had been paying on in now needed to be paid in full. More than the value. T-Mobile says it's nothing they can do. So I paid it in full and another phone I was still paying on. My bill had just been paid in advance. I decided to leave T-Mobile and I transferred all my information. We kept all our numbers just changed our provider. The person that helped me on the T-Mobile end handled the transfer and at the end I asked do I owe anything. They checked my bill said I was paid in full and don't owe on any devices. I'm good to leave and I don't owe T-Mobile anything. So fast forward to 3 and a half weeks later I am charged for a full bill. I'm shocked. I figured it might have been the auto pay. I contacted T-Mobile and I was informed I left 2 days in the new bill cycle. They do not prorate the bill so me leaving not even 48 hours into the bill made me pay a full bill. I asked to avoid this. I asked everything I could and they still find a way to get over. T-Mobile has always been a good phone provider but the customer service sucks. When u finally get a problem it's usually fixable but they escalated and make it so much worse. I've had bills that have randomly went up with no notification. To the point where I had to go call them they had to do research and figure out why it went up and why I wasn't contacted. It's crazy. But this right here feels criminal. Big bill for 2 days with a client that has never been late. Bills paid in advance and in full. Don't let all the small perks fool you T-Mobile will rob you. Please watch your bill and even if u ask the person That works for T-Mobile doesn't mean that they know what they're talking about. Traded in a phone and was told by the person in the store that I would receive a bill credit for the total of the trade-in and was locked into a two year installment of the trade-in value.  There was nothing I could do when the trade was made even tho I was told the wrong thing. Had a buyer for the phone but the t-Mobile rep lied about the one time payout. Locked me in for 2 years to get the full amount. T-Mobile is money hungry