Change your charger get a new one, I had this problem as well. I tried everything turns out it was my charger, I thought it was my port. I bought a new Adaptive Fast Charging plug and a new cable and it charges much much faster. Battery lasts longer as well.
Dear Samsung Member,
Greetings from Samsung Customer Support!
To resolve "charging" issue kindly follow the given below steps:
1. Check charger functionality:-Request you to check the charger functionality with a different device or try to charge the same device with a different charger.
2. Reset the device:-Kindly create data backup of your device via SMART switch mobile application or http://www.samsung.com/in/support/smartswitch pc suite.
Tap on Settings>Tap on General Management>Tap on Reset.
If the issue still persist, kindly register your concern in Samsung Members app (Samsung Members app > Get help > Feedback > Error report) along with Screen-shots(time taken to charge). This will help us to further investigate and resolve your concern.
Note: Please send device log files within 15 minutes of issue occurrence along with the exact issue details.
Thank you for writing to Samsung.
Samsung Customer Support