Garage Door bent & unhinged

On 16/04/2014 I bought a garage door from Kingdom Doors, Xavier, that was advertised in the SOWETAN for R3500, for R5300 after they'd added an installation fee of R1800. On 21/02/2015 two of the door's panels buckled and unhinged, such that the door is jammed half-way, and can neither be opened nor closed. I went to the store at Xavier to report my plight, but the manager referred me to his superior, Sean, at Lenasia. I drove there and met Sean, who told me that there is no way he can help me by way of a guarantee, and that I must pay a further R4000 if I want the door fixed. He told me that it's my fault that the door is bent as it did not have a reinforcement, which should have cost R1800. I was never told about the reinforcement before today. Total cost wud've been R7100(3500+1800+1800). I detest that Sean was unsympathetic. I travelled from Springs to Lenasia, to seek help about a security matter, only to meet an unhelpful businessman who just crunched numbers on the calculator as I spoke to him, blamed me for what happened to the garage door, and told me to pay R4000 if I wanted him to help me. I think this is an unfair business practice.