Change to a cheaper plan with balance on current one.

There's been some drastic household changes in my current residence and I recently picked up the internet bill, which has a balance on it from the person who had it previous. I've already set up a payment plan to help pay off the previous balance because I can't fully pay it off at the moment and at the current rate of the current plan, I fear the bill will just continue to keep stacking before I can pay it all off. So I'd like to change to a cheaper plan but there's no option to change plans until the previous balance is paid in full. I would really like some help changing it to a cheaper plan or help cancel the internet service.