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If you are having a problem with your i phone, the best place for help and advise is an Apple store.
Should Apple not be able to fix the problem with their software, they will replace your iphone.
Apple are very keen to protect their brand. Even though you have purchased the phone from Vodafone, Apple will replace a faulty device and you are more likely to get a new phone from Apple and a reconditioned phone from Vodafone.
Take the phone into Apple and get them to give you the correct help and advise.