Christmas gifts - no exchange?

My son received Mr Price clothing a gifts for Christmas. I received the package via courier yesterday as both parties resides in different provinces ... and unfortunately the clothes do not fit. I contacted the customer service line to enquire if whether i am able to just do an exchange as i do not want a refund. I was explained that i needed a slip for the gifts? how would i have a slip for a purchase that came from someone else in the form of a gift? i live in a different province and only received this package yesterday. The person no longer has the slip. i understand that the process has been explained to me however these items are gifts, they are in an excellent condition and all the tags are still on? i am not asking for the money , i would just like to exchange..