Shares sold at much price than the market price

I sold my existing stock of a company at the market price and it got sold instantly, but the price realised was Rs. 1.50 lower than market price. I again sold shares of the same company and result was the same. Can you explain this? I think something is very wrong here.

When selling the shares, you need to look at the market depth. Check this for example

There is only 21 qty pending buy orders at 1156.5. If you place say a market order to sell 1000 shares, it will go all the way down in the market depth until it can fill the order to sell 1000 shares. So this price at which it is sold, can be completely different to the last traded price.

If you are specific on the price you want to sell, use a limit order.