MBSA *****ing your money on spare parts?

In May of this year I ordered parts for my C-class Merc as my vacuum pump failed. I asked for a quote and the actual vacuum pump (MA***), which was lying in stock in South Africa (Pretoria) was quoted at R5413.19 incl. VAT. I subsequently ordered the part and offered to pay. Because there were other parts of which had to be ordered from overseas and there was a delay I was told I could pay on collection day. This is normal MBSA procedure which I had followed in the past as well. On collection day the vacuum pump price suddenly shot up to R7249, a R1836 increase. The service consultant dealing with the purchase was extremely helpful and tried to reverse the updated price because I had already ORDERED. The head office in Pretoria however refused to revert to the original price. I logged a complaint with customer services and they put the blame on the local service consultants, which was not the case and all they were willing to pay back was R748.50. Meanwhile I have heard that some customers had cases where they already paid on the order and were told to pay in huge differences on collection day. This cannot be legal?