Sell up or sell out!!

Sold me 5 liter's if gearbox oil instead of 3 - why ask my VIN number??? Should this not have been your guideline for the number of bottles i needed with the purchase of my Sachs Clutch Kit. Spent so much money at your branch to be turned away without a blink of an eye by your unfriendly staff member. I want my refund or is your staff trained to sell up on fluids to make sure it does not gather dust...I want my refund...