Trouble with this guest

[Brent H.]

Hi Short Term Experts: what would you do in this situation?

Guest has been on my VRBO calendar for a couple of months

We require picture ID (our HOA is strict about being over 25 years old) (House Rule)

We also require a signature on a short rental agreement (House Rule)

The Guest paid one payment but his second payment is overdue

Guest says he already paid the second payment (VRBO told him he did not)

The reservation came through Expedia since they are partners with VRBO

Guest has so far delayed sending me his ID and rental agreement for several weeks 

VRBO said that the guest says he paid and he will not pay again

I can't cancel his reservation without it affecting my superhost metrics

I'm not sure if he will cancel - because if he does he loses 100% of his payment (unless I give it back to him)

He's probably mad and my 5 star average rating will likely go down (have twelve, 5-stars so far -just getting started)

Thanks for your help! I haven't had any problems with guests, until now.

Brent