@Antony97
Sorry to hear about that, but if you choose a flexible cancellation policy, then you need to be able to deal with guests cancelling last minute with no explanation. There are several cancellation policies available and you need to choose the one that actually works for you and it sounds like flexible doesn't.
I started off with moderate, as it sounded fair to me, but I found that guests were waiting until the absolute deadline to cancel, rather than cancelling as soon as they knew they had a change of plans/changed their minds. They do not think about the impact it has on the host. Their minds are focused on their own needs. So, they keep the reservation 'just in case' for as long as it doesn't cost them anything. This would happen more frequently during high seasons, meaning I lost out on who knows how many other bookings.
So, I changed to strict and never looked back. It did not affect my bookings and, also, you always have the choice to refund the guests extra if YOU feel like it, e.g. if they have a valid reason and you rebook the nights. In those cases, I'll always refund the guests extra, but not if I'm left with unbooked nights and out of pocket or the guests behaves badly.
Believe me, once they are not entitled to a full refund, they will DEFINITELY be in touch to explain why they needed to cancel!