Hifi Corp refunds

Bought a Mi TV stick a week ago, had issues connecting to my router although phones connect without issue. So without there being an alternative, returned it to the store for a refund. They told me they'd like to test it in store and advised them that we don't mind that, however the issue is that it doesn't work for me as the customer. They agreed to the refund with a 15% charge. Definitely not doing business with them again, don't understand why you're being charged as a customer if a device does not serve the purpose you bought it for.