rude sales person refuse to exhcange product

Purchased a laptop bag, was told it would fit a 16 inch, it didn't. I only fitted the laptop in the bag on friday to my shock it didn't fit.bag was bought on 25th june but never used. I need the bag urgently but was refused help. No other bag in the store in my budget would fit my laptop.this is a violation of the consumer act and I will fight this till I am fully refunded.