The way I deal with this is to phone 'em once I've received the renewal notice and say 'is this your best offer, because if you can do better, say so now - I'm going to be phoning a couple of others to check you out'. It usually results in a reduction, having been put through to the right department.
Quite why these people don't realise that it cost them more to get a new customer than retain an existing one beats me. They seem to rely on people's inertia to maintain their business volumes.