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Do you have any insurance on the phone - either with Vodafone or house insurance or a bank account?
A broken screen is not covered by the warranty. You can either get Vodafone to repair the screen or go directly to Samsung and it will be expensive. Vodafone will only lend you a phone if you have their insurance policy.
The screen will cost between £100 - £150
If Vodafone quote you £100 take it as Samsung usually charge closer to £150.
FWIW, I'd also invest in a more solid case - you can get flip-type ones on ebay for practically nothing and they have a rigid back as well as cover for the screen. As phones get larger and thinner they have little rigidity and are more vulnerable to twisting as well as knocks. A silicone case really offers very little protection at all.