Bad service at Zara

On Friday 17.05.2019 I went to Zara at Nelson Mandela square to exchanged dresses that i have bought but could not fit me. the exchanged was done and unfortunately the queue was very long at the fitting rooms and i did not fit the clothes that i have bought.The lady that i was assisting gave me a credit note and not a slip that reflect what i have bought on that specific Day.When i got home and tried on the clothes that i have bought,they did not fit me properly and i went back the following Day and asked to exchange sizes for me everything was still in the bag the lady did not gave the slip on my hand but put everything on the paper bag the only slip i had was the credit note and the Absa slip where i had payed the difference they went through the footage the next Day and the saw the lady putting the slip in my bag but it was not for the clothes i bought but a credit note and they insisted that i have the slip which is not true i must go back and check of which i did but the is no slip now i am stuck with big sizes that i can not use and they can not assist me further.What must i do now?