And in typical Verizon fashion I get this message when using the feature they advertise for canceling service: "We are unable to process your request at this time. Please try again later. We apologize for any inconvenience."
To re-iterate, you're just talking to other users here. None of us have any inside knowledge of Verizon's policies. You didn't provide any information about what they offered you or your old package. If you had done that, we might have been able to help you navigate their system and current policies or given you a bit more insight into why they won't do what you want. But it's clear you didn't want to hear that.
I can tell you that canceling usually requires talking to them. I wasn't even aware they had an online "cancel" button. If that's not working, I suggest you contact them by phone or chat. That should be more efficient then the method you tried.