Complaint

I had a terrible experience at Ackerman's store in Kagiso mall,I purchased a cellphone and the person who was assisting me did not inform me that the handheld device only operates with one service provider's sim card,I had to return it to the store on the seventh day of purchase but the staff refused to exchange it or give me a refund for it,I couldn't use the phone because my sim card was not working in it,I left the phone in store because I cant take it home if I won't be able to use ,I need your help to reach a solution on how I can deal with the matter,the staff there was rude and making bad remarks,it's not my first terrible experience in that store, please help