Problem with Rubine gas hob?

Recently I purchased Rubine brand gas hob. I am facing following problems:-

1) When the gas stove turned off, there is pop sound from the burner before the burner completely stop burning.

2) When the gas stove turned from high to low burning range, there is pop sound from the burner before burning at outer ring stops and burning only from inner most ring.

3) Most of the time when the gas stove turned from high to low burning and then return back to high burning range the burner does not burn in high range but burning in medium range.

4) After turning off the burner, after sometime there is a "tack" sound coming from the knob region.

How should I fix this problems ?