Xbox Gift Card Deactivation

Hello, we have a £50 xbox gift card that is saying 'deactivated' when the code is entered and to 'contact retailer'. Tesco are saying the card has been activated and there is an 'activation successful' message on the receipt. They told us to contact Xbox
We've tried getting through to xbox but can't speak to anyone. The virtual agent is saying it's 'deactivated' and contact the retailer and so it continues .......! Any advice gratefully received :0)

:)