Apple just can’t resist making ridiculous margins from their customers, even when their devices do allow for upgrades to the default configuration.
For instance, with a Mac Pro, you have to pay an extra $800 to go from 64gb to 128gb of memory. For $800, you could get about 384gb of ram in 64gb sticks from a different vendor.
Always demand a human support representative until it gives you the option to, then the actual human will usually manually process your refund if you complain about how the initial refund never happened.
Bonus chance of success if you’re a Prime member and say you’re thinking about cancelling.