Upwork's customer service representatives aren't able to process a refund based on your activity levels on the system. But if you have switched your plan back to basic, we can assure you that charges for premium membership will end.
So it's all good!
I checked your profile and looks like you didn't downgrade to the free membership plan. I'll go ahead and follow up with the team about your concern and you can expect to receive an update via support ticket directly.