I want to erase my old iPhone content that I no long have access to

You can erase the device remotely if you had Find My turned on. The devices would need to have an internet connection.

Erase a device in Find Devices on iCloud.com - Apple Support

Here are a couple of key points:

• If you did not have Find My turned on, it cannot be remotely erased. Did you try the steps provided?
• If you used Face ID with a secure Passcode, then your data is safe. Your device will be disable after 6 wrong guesses of your Passcode.
• If your Passcode was something like "1111" or "1234", you may have a problem.
• You can delete Photo, Contacts, Messages, and Mail that the device saved to iCloud by going to the iCloud website. If you also use the same Apple ID of the lost phones then do not do that, as you will also remove the data from the devices you are using.
• Interested about the call you received claiming that they found your phone. What did they say to you? What did you say to them? Any idea how they would have your phone number? Was the phone number they called listed in your phone?