Faulty product, told I need to settle.

I received a fitbit charge 2 from FNB at the beginning of January. Over the last 3 weeks I have come to notice that the heart rate monitor is wildly inaccurate. It does not serve it's purpose for which I bought it. It is a heart rate monitor that does not record heart rate properly. Hence I expect to return the product which does not work.

FNB are now telling me that there's going to be a cancellation charge! That's not how things work. If a consumer buys a product that doesn't do what it is supposed to from any normal shop, you return it for a refund. It then falls on the shop to take the issue up with the producer.

I expect to do the same with FNB.

The FNB device help gurus have been trained to give one answer...you return, you still pay. Please can I speak to someone who's capable of making decisions and resolving the issue of a product I am morbidly unhappy with.