Ecomed - Non-existing Customer Service

On 17 May 2018, I bought my mother an oxygen machine from Ecomed in Pretoria. A little more than a month later (end June) the machine broke. Since it was a brand new machine and still under guarantee, I phoned Ecomed and they came and collect the machine and brought her a second hand loan machine. They told us it will be repaired, but if they are unable to repair it, they will exchange it for a new machine. We are now in Oct, more than 3 months later, and and still no answers from Ecomed. I phoned numerous times and even once spoke to the technician himself. Still no answers!! Surely, if it take more than 3 months to be repaired, it cannot be fixed, so I demanded that they replace the machine. Everybody told me they must first speak to their manager (for the machine to be replaced) and then they will phone me back - nobody phones back! I am at a loss at what to do next - one pays a lot of money for such a machine, and the service one gets afterwards is non-existing.