not happy about their service

I bought my sound equipment in December 2015 worth R20 000.the sound included 4 hybrid top speakers and 2 double bass bins. A day after delivery,I noticed a funny noise on one of the bass bin,when ever I pick up the volume,it would sound as if it was damaged. The following day I called fastrack germiston and told them what the bass bin was sounding like,they suggested I bring the Base speaker back,when they checked it,they found it has a factory fault,I asked them to replace it for me because the sound is still new and it's not my fault it is not in good condition,they told me they don't have stock of a replacement for the faulty speaker,they manager suggested to take it for local repairs,with hope I thought their repair was going to be good.i went back with it to go fit and use,as I played it,it still was not properly fixed up,i called them to explain it's still making a funny noise. They told me unfortunately they can't help me any further. Today I decided to open the speaker and see what it the problem, then I noticed their repair that was done by fastrack store was to put glue on the speaker and the alignment was not properly done,so the coil was touching on the piston,basically means the factory fault was not repair. I am very angry because now they want to charge me R1400 to replace the speaker that I've been complaining about for months. I want something to be done about this issue,we customers have to suffer for their mistakes.