Is 20 Aug. by chance the same date after which the request can be escalated to a case? If you view the return request in eBay it should state this somewhere.

Yes, it's that's normal, but as Countess pointed out you don't want it being escalated unless you know it's going to go in your favour.

I'd be getting back on chat, hopefully finding a different CS agent, and trying again to get a commitment from them in writing.