AirPods are not connecting

I have the 3rd generation AirPods and I can’t get it to reconnect to my phone, I had to disconnect them because the left one wasn’t working so I pressed forget but the connect page didn’t appear when I tried to connect them again and nothing appeared in the Bluetooth list. I have held down the back button to reset them, I have opened and closed the case. My phone has the latest software, it’s an iPhone 12. The support page where it says how to connect and reset them didn’t work. Apple support couldn’t figure it out either. So I put them on charge and left them for a while, I opened the case and the connect page appeared, I said connect and it said that the AirPods were not my AirPods and asked me to hold down the back button and reset again ! I’m not sure what’s happening.