Can a cable company charge me a cancellation fee and take away the discount they were giving and make me pay the difference ?

hello, I recently changed cable company's. I was uncder contract with another company and acured a cancellation fee. The company prorated my account for the month I canceled. when doing so they also took away the discounts the were giving me. The company wants me to pay the difference in the discounts as well as pay the cancellation fee. is this legal ? Can they take away the discount and make me pay the difference and then pay a cancellation fee ?