I am happy to report that after two days of complaining with friendly admins, who cared enough to push the support team, and after a couple of publications such as this thread, Gate.io has adjusted the withdrawal settings. I have been succesful in withdrawing my RBTC!

The minimum is now 0.10005 RBTC with a fee of 5.0E-5 RBTC.

Thanks to all responders for the support. It made me feel less alone in this matter.