Invertor MECER

I returned the mecer i have purchased from Builders since the battery did not work, On my enquiry on when the battery will be replaced , i was informed that since i was negligent i need to pay Some amount of R 2k plus for the replacement battery, which i did not do, i was then informed that if i want to collect the mecer i need to pay R160 before it will be released from Mecer agency, which i did not pay, i bought this product at Builders, i took it back to Builders, I need Builders to honor our agreement when i have enquiries because of a defect. Long story Short, i have received the mecer back yesterday just to find out that the one that was returned is not the one i returned, the serial number is not the same, and the question is that where is my product that was given again to builders / mecer to be fixed. The state in which this SECONDHAND product was returned to me , leave me to think that mecer does not care about their brand. That the repairs of my product was not done as i requested under warranty to be done. I am returning this product again today and want the one that i return to be in working order back to me. If my money was good enough when i bought it , surely the after service for a defect need to be honored by Builders or Mecer , the product they are selling. I have mailed Builders informing them i am returning the product today, and will give them 15 days to sort out this.