That depends on what type of mobile phone it is, and how long you've had it.
I have an iPhone.
iPhone customers benefit from a special care service provided by Apple directly. Please call the Apple customer service department on 0800 107 6285 or visit their support site to troubleshoot your problem.
If you have a refurbished iPhone, please see below.
I don't have an iPhone.
Mobile phones are covered by a manufacturer's warranty. So if your mobile develops a manufacturing fault within the warranty period, you can get it repaired or even replaced for free.
I've had my mobile for more than 30 days:
Please contact your manufacturer directly. If it's still under warranty, they will support you with a repair or exchange.
I've had my mobile for less than 30 days:
If we can identify the fault, we'll exchange it free of charge.
If you have a refurbished mobile phone, please see below.
I have a refurbished mobile phone.
Refurbished mobile phones are covered by a supplier warranty. So if your refurbished mobile develops a manufacturing fault within the warranty, you can get it repaired or even replaced for free.