How to complain about a rude support agent?

I had a phone call on 18 April 2023 around 10:40 am (EST) with a representative who called herself as "Jay" for the following issue: message on my settings in my iPhone, which says "This number is registered to your Apple ID but is not associated with this phone. You can keep using until it expires" The expiration date shows in 4 days. Jay told me that it has nothing to do with Apple and it means T-Mobile will cancel my number in 4 days and said that according to her experience it happens all the in the US (!). When I said it doesn't make sense, trying to explain her the situation with my phone, she started to lecture me on a totally different issue, claiming that eSim and Sim-free are the same things and started to get tense and cut me off when I am talking, raised her voice and when I wanted to file a complaint about this service, she claimed that she is a high level supervisor and there is no one above her. So, I called again and connected with another representative who is so nice and resolved the issue just in 5 minutes. Even another agent resolved my issue, I want to file a proper complaint against this "Jay" person, if this is her real name, as she should be trained on how to approach clients and how to resolve the issues.