Disgusting service from Vodacom

I bought a charger for R400 in January which worked for 2 weeks then stopped working on my phone. I then took it back to the shop and they swapped it for me. I have been returning the same charger for the past month and getting different chargers which work for a couple of days then stop working again. I was informed I cannot be given a refund because of a 7 day return policy on electronic devices. On one of the occasions I visited the store they did a SW upgrade on my phone but still their chargers stop working after a couple of days. This is the most pathetic service I have received at Vodacom in all my years. What about the petrol and time I spend each time I visit the store for this R400 charger???