Vox is slowly become a ****

I really need clarity on something. When I took out the Vox contract, the selling point was cancel at anytime... I cancelled the contract on the 15th of September, which according to the TORs it should take 30 calendar days. They now insist that 30 calendar days only mean from the 1st of the month to the 30th of the month. What are calendar days if they cannot start from date of canceling and then pay pro-rata for if required?