@Michael-And-Helen0  Lovely place!  As to cleaning fees, there is some debate about that as some hosts think it is off-putting to potential guest who assume that cleaning would be included in the nightly rate.  
 
As to your issue, you get a copy of what is being charged to the guests and if there is a cleaning charge, you would see it on your reservation confirmation.  It is possible the guest is mistaken.  However, if the guest gives you proof of a cleaning fee being charged (they can show you the booking confirmation), you should contact Air BNB as there may be a glitch in the system.
 
Here is a guide to contacting Air BNB
https://community.withairbnb.com/t5/Help/Contact-Airbnb-A-Community-Help-Guide/m-p/16165#M728