Refund

I bought 2 pairs of shoes online in December but i had to return them because they didn't fit me i followed all the instructions that was given to me. Now when i enquire about my refund i m told that i returned one item but i returned 2 item and the courier company signed for those 2 items what i dont understand is why is it my problem because they should check with the courier company that they used to collect the shoes from me.