Okay, if you haven't got anywhere by now, here's my advice. Do not do any telephone calling. Put everything in writing. Write to the Store Head Office- Managing Director, copy to Branch store Manager, copy to Consumer Affaris. Attach copies of your bill and any correspondence. In your letter give them a 7-day deadline to respond.
Make sure to deliver the letters, either by hand or by post, and make a note of when you post them. It is better if you hand deliver, so that you can get someone to sign for receiving, otherwise you send the lettersby registered mail. Yes you can do that for inland mail.
You will get a response.
Do not give up. By law you are entitled to redress.