Rain Customer service

I upgraded from my old 4G sim to the new 5G sim over a month ago and after receiving the upgrade I've tried calling and emailing several times to cancel my old sim to avoid a double payment seeing that they dont do it automatically from an upgrade and everytime I get told someone will be in touch. I've been waiting and contacting for over a month now and what I feared has happened I'm being billed for both services. I refuse to be held accountable for there poor Customer service and lack of communication.