@Sher6
I think the thing you must understand is, the Airbnb platform runs automatically and simply responds to commands within certain perameters.
If the guest booked at a certain price.....that is the price you must have set in order for that booking to proceed. If that was not your set price then the booking would simply not have been accepted by the system.
Sher, you cannot blame Airbnb for things you have not set correctly. Having worked in support I have seen this occurence thousands of times, and in each incidence it is not an Airbnb issue, it is a host issue because of some minor detail they may have overlooked.
If however you are in this instance sure of your ground get onto Airbnb....the contact phone number is a Sydney number and it is 02 8520 3333 and if it is their error they will correct it for you.
Cheers......Rob