HELP! Unknown Phone Number Added as OTP – Locked Out

Attempted to log in to my main SC account last week and was asked for an OTP (we have 2FA set up and always have). We’ve previously had 6-7 different phone numbers (many users) for the OTP, and also had the Authenticator App set up. However, it no longer is giving us the option to select the App, and it only lists a single phone number that we don’t recognize.

I’d request the OTP to the email address, even after inputting the OTP it would ask me for a second OTP from the unknown phone number.
Went through reaching out to Customer Service via the link provided and they gave me instructions for how to disable 2FA on the account, but they don’t understand that I can’t do that if I can’t access the account in the first place. It’s very odd, seemingly came out of nowhere — we were able to access our account with zero issues until last week.

We’ve tried 2FA reset process, password recovery process, and every other “suggestion” provided by Seller Support, but nothing has worked because each process still asks me to log in and provide the OTP from the unknown phone number. Support has transferred (3) cases I’ve opened about this issue to an “external” team doing an “investigation,” but I haven’t heard anything back from them in days.
We have secondary users set up who can access, so we’re still able to deal with customers, orders, etc., but we have to get access to the main account because this whole scenario is concerning. I’ve searched the forums and tried every solution provided by other sellers, but nothing seems to work.