Grimlin I've been using https://silent.link for a good while now and they work well. You don't have to give them any data, not even a mail address, their website is Tor-available and you pay with BTC or XMR (preferably the latter for better anonymity). Your eSIM is always in roaming mode which reveals less data to the network provider, too. It's all you can ask for if VOIP is not an option for you.
Be aware that you still use an eSIM, which is inherently not anonymous or private (you're on a tracking network, the SIM can read your hardware identifiers, data is unencrypted etc.), but at least you don't give any personal identifiers away in the first place. Being a roaming prepaid SIM, you most likely need to fiddle a bit with connecting your network manually or switching roaming profiles for it to work at first or when crossing borders.