I've gotten 'bills' (well, the insurance company telling me I owe a provider some money) for services that haven't been rendered! Just because my provider tried

I've gotten 'bills' (well, the insurance company telling me I owe a provider some money) for services that haven't been rendered! Just because my provider tried to pre-approve something and insurance denied it but the letter was phrased in a way that implied I was on the hook for it. Luckily a call to my doctor cleared that up.