MAG

why is ∫dl = 0 ??

infact that is 2Ï€R (if your direction is along the loop)

∫dx over the loop is zero
∫dy over the loop is zero
but ∫√dx²+dy² over the loop is not zero

and net force is not zero.. because the force is a vector.. and one component of the force are not distributed such that the forces cancel each other...