Angry Telkom customer

I took a Free me 1gig contract with Telkom in Feb 2018 and the device was delivered on the 7th Feb 18. The device was faulty and it did nt work properly so i cancelled my contract within my 7 day cool off period because they wanted to repair the device instead of sending another iPhone. I had to deal with the *********** after sales agents who could not assist until i requested to speak to their manager. Nkosinathi Mhlongo their Manage assured me that i will not get further charged by them since i cancelled the contract within my 7 day cool off period. The phone was taken by the courier company and returned to Telkom before the 14th of Feb 18. On the 9th March i received an invoice from Telkom stating that i need to pay them R272.38 by the 03 Apr 2018. Mind you these charges are for March. The phone was taken before the 14th of Feb but i'm getting charged by Telkom for March.