Cancelling Auto-pay

I will be switching to a different service that is better for me financially. In order for me to keep my number with this service the GoPhone account still has to be active. My auto pay renews the 4th and I don't receive my sim card for the new service till the 8th. If it went through with the $45 I'd have to wait till next month to switch. I was trying to figure out if I would be charged if I stopped the automatic payments. I couldn't remember if this was a non-contract service.