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You may need to use a postal service if there is no centre near you.
3rd party repairers such as CarPhone Warehouse are governed by Samsungs Terms of repair.
However Samsung themselves are more lenient, unless it has actually been dropped into water then you will have Void your Warranty.
You could look into your Household insurance for accidental damage?
Don't mention water to Samsung. Let them find out whats wrong with it.