Change plan issue and retention of current plan

I made a phone call to customer center to change and downgrade my plan with student offer, and he said that I had to cancel my current plan and then resign for the new one. So he helped me with canceling my current plan and I got the email that xfinity is processing my cancelation. 
But as I revisited the promotional booth near by my home to resign the lower plan, staff said that I cannot get the student offer again for the downgraded one.. 
It is quite different from what I heard when I purchased the plan that I can freely change my student plan within 30 days, and also from the phone call, he said that I can resign for the new one among the student offers.

So I think I have to cancel the cancelation of my current plan and keep using it for a while. 

And I have more question regarding the payment, if I cancel before my autopay date, I only pay for the deposit, not for the rest balance charge?