DON'T EVER buy a phone cash from Vodacom it's a TRAP

I bought a Hauwei P40 Lite at Mall of the South for R6000 and when I wanted to exchange the phone the following day I was told that they don't do exchanges and I can sell it back to them for R4000. How can a phone depreciate by 33% within 24 hours and they don't even look at the condition of the phone. Which pricing model does Vodacom use???? Vodacom doesn't allow us to exchange our phones within 7 days. DON'T EVER buy a phone cash from Vodacom it's a TRAP