2 month old phone not fast charging

Good Day Vodacom, I've been asked to take my phone to Samsung repair centre in Umhlanga which is about 25km from me and if the store sends it then i wont have a phone for about 2 weeks. This phone is 2 months old and under warranty and no one in technical at the store can tell me whats going on, why must i be without a phone for 2 weeks, and why cant this phone be changed under warranty as i also use this phone for work. My phone is a Samsung A54 and does not fast charge anymore. I bought the original charger from the vodacom store when u got the upgrade done.