SONY 55 INCH TV - Warranty delayed by Sony India

I bought a Sony Bravia KD**X**K on * Jun **** and have raised concern over the performance issue via their service centres. However, the TV performed fine when the technician visited the house * times and hence I had shared videos showing the lag and booting issues. The issue always existed but the case was closed at their end since they could not identify the same when they visited.
Now after the warranty is over, the team is responding stating they will charge me for the repair where the motherboard shall be replaced.
They also question me stating how am I so quiet while this issue existed until now.
My question is, why is this diagnosis not done when they visited me * times and check the motherboard at that time?
Now why would I pay Rs. **,*** for this repair while I paid a whoping Rs.**,*** for this TV?
They also claim that X* is the best performance processor at that time, then why would it have performance issues?
I did not get any grievance redressal email ID for Sony. Hence writing in this platform.
They now want me to confirm the repair with the cost before * March ****. What kind of a bullying is this by Sony?