Can you still retrieve that invoice?

Does it still show 1BjzEH9v3CvsrGPjsW7e491KJdCBQF6wpw as the payment address?

If so, then clearly the invoice was paid and this just seems to be a simple administrative error where BitVPS just needs to figure out where the problem occurred in applying the credit for the payment.

If the invoice shows a different address, then there is a different problem to solve.