Yamaha Motor India — Self start trouble

Hi my name is adarsh pg i bought a nee mt 15 bs6 it has 4 months old now.
Now the problem is it was not starting properly mainly the problem appears when i takes tha bike from direct sunlight. That time it was hard to start.
I complained to the service center they took my bike and told me that it has no problem i told them that take my bike and chek it after resting some time in direct sunlight. After they realized that my bike have starting trouble they took my bike and some hours after they called and told me that the issue was solved. But the next day i faced that problem again what should i do? . What is the reason that my bike was not starting i am trusting your brand .hoping to hear a positive response from you