No response from Avis - Can't get through to call centre

I received an email and SMS saying that I had an insurance replacement rental (which I do not) and that I would be charged if it was returned on the day I received the notification. I have called several times, but cannot get through to your call centre - no answer!! I have emailed several times as well with no response. I'm concerned that this is either ***** or a mistake on Avis's side and that they are going to take money from my credit card. But I can't even speak to anyone at Avis to try to resolve.