Duplicated Costs

During February 2015 I contacted the Telkom customer care to request an upgrade and the Call centre advised me that I need to upgrade at a branch/store. I then proceeded to the store in stadium on Main, Claremont and they didn't have stock of the iPhone 6. I was also told by the Clerk, that the Call Centre advised that my upgrade was due in March 2015. I couldn't understand why they gave me this feedback as my month 22 (Due for an upgrade) was actually February 2015 as my month 1 was May 2013 as Telkom does not apportion device costs and deducted the full device cost for the latter month. On the 2nd of March the branch still didn't have stock and only then the approvals team accepted by Upgrade request. My contract was signed on the 6th of March 2015. However, at the end of March I was still billed for the old contract, Z10 and at the end of April 2015 is billed again for March 2015 on the iPhone 6 and for April 2015. This puzzles me as how can you bill me for a full device cost for March 2015 on my old contract due to your lack of stock and tracking of the months on my contract & you still billed me again in April for March & April device and usage costs on the iPhone 6.