\Device Installment Fee"not charged pro rate"""

I have recently taken out a contract with Telkom Mobile for the Sony Xperia M5 on Smartplan 100 advertised at a monthly rate of R369. This contract was signed on the 30th of November, on the 3rd of December I received a invoice amounting to R642.30, for the month of November and December. On the details page the monthly amount of R369 is composed of 2 entities: R270 (Add On Device Installment Fee RC base) & R99 (Smartplan 100).<br> On my invoice I paid pro-rata on the R99(Smartplan 100) fee(R3.30) since I was only 1 Day of November in the contract, However I paid for the full amount of R270 on the device installment fee even though I only had the device for the last day of November.<br> I asked the billing department at Telkom (Menlyn) who could not give me a clear explanation, I then attempted the call-center who also failed to clarify. Finally I used the chat function on telkom's website to verify from a consultant that this particular fee is not pro-rata and he confirmed that I would've save R270 taking out the contract on the 1st of Dec rather than the 30th of Nov.<br> This was not explained to me when signing the contract and could certainly not be deemed fair towards customers?