Poor service!!

Extremely unsatisfied with the service received. Ordered a Nike runner in size 10, received size 11 in the delivery. Contacted the call center same day for an exchange for the correct size that I initially ordered. They do not have the size in stock. My question is, where did it go? Because when I initially placed my order there were size 10s in the warehouse so I am expecting the size 10 that i paid for to still be at the warehouse. Very disappointing that it is Festive season and we are shopping online for Christmas gifts and this is the service we get.