Refuse to replace faulty charger

I bought my Note 4 less than 4 months ago. The last 2 weeks the fast charger has been acting up. All other chargers work. But this one constantly goes in and out of charge. Almost as if the connection is bad. The store clerk refuses to replace it. I must either pay R350 for a new one or send my phone and charger in. He also tried to peddle cheap generics. While I have tested it to be the charger's fault. I feel I should have the charger replaced without charge seeing as it was not my fault to begin with and I've hardly had the phone for a short while. The attitude of the store staff leaves a lot to be desired! Not the 1st incident that leaves bad taste in mouth.