Expired Credit note

I went into Truworths Centurion this afternoon to spend my credit note that I was issued a few weeks back after returning an item, to be told that my credit note had expired. On the note it states that it is valid for three months from date of purchase. The purchase date stated 6 March 2015, and today is the 26th of May, it should therefore still be valid until the 6th of june? I was furious and so went to Truworths at the Mall at Reds as the Centurion branch was rather careless and refered me back to the branch that initially issued my credit note. The staff at Mall ar Reds were amazing and tried really hard to assist me, to be told by their head office, regional manager ect that my credit note was initially created on my very first purchase, apparently the 23rd February! Sooo not only did this date not reflect anywhere on my credit note, stating its validity for three months, I was only three days late and they still refused, at head office to do anything to assist me! So what they just decide to keep my R205 and I must be okay with that? My new purchase was over R200 more than what the note was even worth so they just threw away a sale and a customer.