Sophisticated scammers know how to do this, I am obviously not going to explain how on here.

All you need to do is open a case for item not as described and, if provided with a return label, send back what you collected.  The scammer will not want their actions under scrutiny so are likely to just agree the refund and write this one off as a failure, hoping to catch others.

Don't open a case for item not received, you will lose and then need to appeal, which won't be necessary if you open the not as described case.  The scammers will be hoping this is the case you open, which you would have done if you had not been able to collect the parcel.  To be honest you were lucky RM gave you the address, that was actually against the rules.

You could let ebay customer service know what has happened separately to the case, but you won't know what action, if any  they take.