[mothered]

According to what the rep told me, they ask for it to open an investigation: "- A copy of your ID with signature so that I can open an investigation with the carrier (you can hide sensitive information such as date of birth on the photo)."

That's total BS.

You've already ID'd yourself when your online account was created - that's why you're able to purchase from their site. They don't require further Identification to start an Investigation. They have all details about the account holder (yourself) at their disposal.