How to Unsubcribe for 8x8 Free Trial

How do I unsubscribe for 8x8. Each email address I email to return saying the email is unmonitored. Been trying to do this before the free trial I signed up for was expired. Now the first payment was taken from my credit card and I do not want a second payment taken from my card. I have not been able to get through by phone.
I signed up a quote form and no response. This is 8x8 was advertised on the sent me a payment receipt with an email that I cannot reply to.