Hello Sachin, I didn't myself have had any trouble with the Ergo's switches, but I did with other mice. The solution to your problem would suggest a problem with the switches. Since I don't have specific experience with the Ergo switches, I would suggest you search on iFixit "switch Logitech". I noticed there are some fora discussions and also instructions on how to replace the switch (if it comes to that), which parts to use etc. I'm sorry I can't give you a straight answer. Good luck! Eiti * If you do find a solution, please post it here. I'm sure I (and others) will eventually get to the point where my Ergo will need some work on the switches. Even if you don't want to go through the trouble of taking pictures and writing a complete instruction, just describing your solution as an answer here would be very helpful.
By your message, it isn't clear if the wheel stopped "mechanically" rolling in one direction or if it doesn't respond (on the screen cursor) to the movement on the wheel.
If it is a mechanical problem, I would check if the torsion spring (the metal part near the wheel) is correctly nested.