Let me clarify why you are not able to get rates for UPS SurePost,
UPS SurePost is not able to return rates via the API. You can only get a "shipping cost" returned when you create the label.
This is due to SurePost needing more information than the basic to and from postal codes, weight, and dimensions contained in the Get Rates call in order to accurately return a rate quote. Because of this limitation, we're unable to provide SurePost rates via the API GET Rate call.
I too have the exact same issue.
And, like you, I have heard nothing from SS in terms of a resolution.
SS support is among the worst in the industry.
Their "chat" agents are excellent, but if they can't fix the issue....good luck. "Senior Support" seems to never follow up. I have support cases open over a year.