Do yourself a favour and don't waste time trying to get them to explain it. All you will do is get agitated and run up your phone bill. I wasted many hours and fretted over similar query and got lots of different explanations from different members of staff including ....
New policies are not for a full 365 days as 1st 14 days not covered for illnesses
All renewal premiums calculated by reference to claims made nationwide that Axa have had in 30 days prior to renewal for your particular breed of cat
blah blah blah........ and other such nonsense that will never explain such a large percentage decrease....
I've just had renewal through for Noni which is acceptable for once. As it is paid monthly, it seems to suggest you don't have to bother phoning to renew but I don;t trust there admin at all any more so will ring anyway. It's just taken 2 months to pay up on Freddie's last claim. 1 month delay due to vet and then another month for Axa to deal with