Failure to Accept Truworths issues credit note

At the end of June I returned items given as a gift to Truworths in Brooklyn Mall. As I did not have a receipt, since I was not the purchaser, I was issued with a credit note. It was NOT explained that this note expires or must be used by a particular date. There is nothing on the actual credit note stipulating an expiry date as well. On Friday, 30 October, I went to purchase an item and wanted to use the credit note, valued at R320, for part of the purchase. I was then informed that the note had expired as it was only valid for 3 months. The manager, Jimmy, said that the cashier who helped me in June remembered me, and she know she explained their policy, as I have a Truworths account. Except I do NOT have an account, so she must have NOT remembered me. Either way, the manger basically told me I was a ****. Jimmy claimed to have called head office, who basically said too bad, there is nothing they can do. How can they claim a credit note expires when nothing is printed on the actual note and the cashiers do not explain it to the customers either. This is basically a ****. The cashiers/helpers in the perfume area said this happens often.