There is no phone number that works that I know of these days, BUT you can basically just try to find one of the Seller Support issues that will allow them to call you (they will call instantly), and that’s how that works.
If the specific topic that you need help on doesn’t have a Callback option, just try to find one that does, and then have them transfer you to the right place.
I will say, they will almost certainly not send you to Seller Performance. However, if you ask for a “Leadership Team Member” to help you, and tell them that you were told by email from Amazon to contact them, then they may actually do their job and transfer you to a competent person. 🙂