I've had this twice. Once with oracle, once with azure. They both charged me $2000-$5000 for simply opening and closing a database instance (used only for a single day to test a friend's open source project)
To be fair, support was excellent both times and they waived the bills after I explained the situation.
How did you run up a $5000 bill for just testing a project? What kind of project was it that could put so much load on the DB?