@Mary-Alice3
you main problem is that you set a strict cancellation policy when you are not able to apply it.
Strict cancellation policy is for strong host who know how to be respected by travellers and Airbnb.
Not for them you repay just because the guest ask for it (never mind how they ask).
I suggest you to change for a moderate cancellation policy.
So you can propose to cancel the reservation and they will by repaid of 50%.
If you are strict enough, it helps them to cancel or they will loose 50%.
If you are not strict enough, use the flexible cancellation policy because it is your way of hosting.
I am not afraid of reviews because i always write objective review.
So if the traveller does not want to have :
"Bad experience. X did not read the listing carefully before booking and asked for a full refund for his own failures.
Place was left clean (or dirty). House rules respected (or not).
Be careful if you receive a request from X. Check he carefully read the listing and he accepts the cancellation policy".
I am not sure he will be very successful with other Airbnb hosts.