Have you tried asking them through the chat system? I had a similar issue in November - took a number of weeks, but it DID come. The interest due in February came without a problem, so my faith is restored. Keep in mind that the 1st April was a bank holiday weekend, so I would have expected a delay of some kind. I would recommend talking to Live Chat via Chip Chat - they’re usually very helpful.
As ever, if someone wants to start off their Chip journey with 1% interest, feel free to use my code: MT90V9 (full disclosure - I also benefit)