I would suggest attempting to get PGE to send you something on their company letterhead stating that, "Yes, you can charge from the grid while connected to PGE and also setup with net metering solar".
If that is what they told you "yes" to, then they should be willing to send it to you in writing. if they do that (I doubt they will, but if they do), then you take that document and ask tesla to enable it for you.
Failing that, tesla isnt going to enable grid charging for you while you are connected to solar, regardless of what you got in an email.
Seems first thing you want is in writing something from the IRS