Delivery delayed because they ask more money.

I ordered a generator per Internet from Gen Power Supply [URL Removed] on Thursday 23 April 2015. After I paid for the generator and the shipping on Friday 24 April, I received an e-mail that they will send me the details for the delivery on Monday 27 April. I get that on Monday and when I used the tracking number, I saw that the delivery will be on Tuesday. On Tuesday morning I received an e-mail from the courier company (Freight Mover Services) and from the supplier to tell me that I need to pay a further amount for insurance (R3880) that will be refundable once the delivery is done. If I don`t do that, they will not deliver my package that has been fully paid along with the shipping. I don`t have the money and cannot see why I need to pay for something that has been paid.