The ordered product is repeated!

I use firebase, but I let customers adding there products in a "App state" cart variable.

, as follow:

Now, look at the following image:

The order "product" is repeated when I try to buy more than one piece of a selected item rather than appears as number such as when I add tow pieces of a product to the cart the massage that appears to me should be "you added 2 pieces".

So, when I add the item to the cart and I want to more than one piece of it I simply press on the + button to add more with no repeatition of the item as showed in the last image rather I want to put number of Item I added to the cart "you added $num of this product".

So, please, how to fix this problem?

Thanks alot.