How did this happen?

[Whingey]

Asked for points on nectar card to pay for shopping and no points. Told cards get cloned and call number .out of service.

Have you tried logging in on the Nectar app? You could check there, and if there's still a problem you can use online chat there too.
Do you have any recently old receipts with your card balance on too? This could help dating when the loss may have occurred. If it has.