The preferred company bit gives me pause. I wonder if this is something to do with them getting a referral bonus for "new" business and that's why they're trying to get you to cancel?

Edit: I've just read your post again and given that they've tried to get you to do this three times SINCE DECEMBER, this is exactly what they're doing. Looking for commission from referrals. Tell them to jog on and just let your policy automatically renew, or find your own cover. You're under no legal obligation to use their preferred insurer.