Unprofessional personal and not doing as what they say

i was quoted R200 a battery for a garage door over WhatsApp by an employee I then send a friend to collect and was charged R300 per battery (33%) more. When he send me the invoice i have queried the amount and they said he did not mention the R200. I have phoned several personal including the manager and owner ( Kobus )and they will just not honor the price they gave over the WhatsApp message. They also did not want to take back the items as the do not return batteries. the batteries is still with my friend. unprofessional, rude and not being truthful. For me it is commonsense if one sales person quote and my friend did not mention the price and a different sales person sells it for 33% more surely you as owner should do the reasonable thing in refunding the difference. I guess that is not how they do things there