I've just looked at your listing and there is no evidence that you cancelled a reservation which is normally indicated by an automated message stating the host cancelled the booking.
Also cancelling a booking does have an impact on your super host status see policy and T&C below. However that said, this is all happening at the moment and Airbnb and only just doing their July 16 assessment at the moment so very much doubt it has impacted your status as this reservation has not taken place as yet and there is no evidence of a cancellation; your July assessment will be based on you completed activity over the last 12 months.
https://www.airbnb.co.uk/help/article/990/how-do-host-cancellation-penalties-work
https://www.airbnb.co.uk/superhost/terms
Re the double confirmation, is it possible that as opposed to sending you an alteration request, that the guest has sent you a new booking request for July assuming that the original September reservation has been cancelled as per the conversation between the both of you? When you go into your actual calendar, can you see this guest booked in in both July and September 16 as well? If you can see the guest book in for both periods still then I suspect they sent you a new request.
It is probably best if you contact Airbnb directly to resolve this one as they will have direct access to your account so can check exactly what is going on as all we can really do here is speculate and the guest's arrival is imminent so you need to know where you stand. Click on the link for contact options - Contact Airbnb
Hope you get it sorted soon.
Ama
