There is a 2 year warranty on most Samsung devices, or a contract-long EE warranty on any phone bought on a device plan from EE, provided there is no physical/water damage to the device or anything else has been done to the phone which would void this warranty.
A repair can be booked in by EE over the phone or in a store (where it will be sent to a nearby EE Repair Centre Store or the central repair hub, depending on your location) or via Samsung directly. This will be free of charge as long as it is a manufacturing defect and the warranty is not voided by any of the above. On inspection if it is deemed to be physical damage caused by the user, the warranty would be voided and it would become a chargeable repair.
Phones are not exchanged under warranty, outside of limited circumstances where a manufacturing defect has rendered the phone unable to repaired, or if an issue occurred within the first 30 days of purchase.
The site detailing EE's repair service can be found here: https://ee.co.uk/local-repairs
Your nearest EE Stores can be found here, including which can book repairs and an estimated turnaround for a typical repair booked in at this location: https://ee.co.uk/store-finder
EE also have a Help article for if you are having issues with your device: https://ee.co.uk/help/mobile/fix-problem/i-have-a-problem-with-my-device
