New contract

I was approved for a cell phone contract. I ordered the Samsung A6 plus in Lavender. I app**** for acontract online for R349.00 I went through the process to get my number ported. A sales consultant called me for the delivery address and told me that the debit order of R349.00 will go off 24 hours after my new SIM card has been activated. That would then be on the 20th of September. How does it make sense to charge someone the full amount for something they have had less than half the month and why not the pro-rata amount? I was told then to apply for the contract again at the end of the month. Now the price for the contract is R489.00 for the exact same phone.