Buy and Paid but can't load it

On 19 Sept we travel to Klerksdorp to buy some mechanical equipment. The salesman told us that we can't paid by cheque(no signs in shop). I go to my bank and transferred the money direct into their account. The bank give me the proof of payment with a stamp on to proof it. Back at the shop they told me that it proofs nothing, the money must reflect in their account before I can load it. I must wait 48 working hours. We must go back home empty handed and more than R30 000 less in our bank account. They let me feel like a *****. They make a big issue of it in front of all the shoppers. Now I must travel again 600 km to fetch it on my cost. I WANT TO KNOW SINCE WHEN IS A BANK STAMP PROOF OF PAYMENT NOT MORE A PROOF? I feel they must courier it to me on their cost, because they kept my equipment after I paid it in full and give them the proof! IF A BANK STAMPED PROOF IS NOT A PROOF ANY MORE - WHAT IS THEN A PROOF??? The senior salesman - Ettienne was not handled it correct and have to apologise to us in the public.(We are not *****s and if we was why will we paid it and show them the proof?) he told us it is instructions of headoffice. Maybe they also have to appoligise to us.