How long before I can apply for bill credit after switching to virgin?

Hi

i switched from sky in November. Awful experience for several reasons leading sky to argue with me about early termination fees which were applied during a golden my off period. Was told by virgin I could claim £200 in credit to cover the switch fees. Since then I’ve been told to expect an email with instructions but nothing, chat function takes ages so I’m trying here to see how others have done it. My sky account was closed mid November so I’m a bit annoyed virgin haven’t at least told me how to apply.