Is this sentence grammatically correct?
"Vodafone are providing a useless service"
I am quite sure that the Vodafone is singular, but everyday I see even many native English speakers using the Are instead of the Is
A company such as Vodafone can be considered to be a large group of people, therefore plural, or a single organisation, therefore singular. So you can use either:
"Vodafone are providing a useless service" is equivalent to "The employees of Vodafone are providing a useless service".
"Vodafone is providing a useless service" is equivalent to "The Vodafone company is providing a useless service".