Bad customer service

I am very disappointed in the service I’ve received from Titan Green Tech / Titan Air-conditioning. Had a Jetair aircon installed, worked for 10 days only (Installation was done 13/12/2019) Did notify them in writing 13 days after installation (26/12/2019). Also tried phoning, left messages and sent e-mails, which was all ignored. After writing a review on google about the service I got, i received a message that I can get someone else to repair the unit. The unit is still under warranty? And they now claim that I’ve only notified them on 29/01/2020. I can not recommend at all. I’ve really tried to be accommodating and patient for them to resolve this, but to no avail.