Here you should stand transparent in communication, effective communication iits quite vital and of importance in such situations. Aim at regularly providing updates and progress on your channels of communication, this helps to keep trust between your customers. Mind offering solutions to disruption caused while offering explaining clear expectations of improvement in it. Intelligently emphasize with customer frustration and find on an appropriate way of offering compensation in future.

From my experience, Subject: Service Disruption Update Dear [Customer Name], We are writing to provide an update regarding the recent service disruption you may have experienced. Our team is working diligently to resolve the issue and restore full service as soon as possible. [Provide a brief explanation of the cause of the disruption and the steps being taken to address it.] We apologize for any inconvenience this may have caused and appreciate your patience. We will continue to provide updates as the situation progresses. Thank you for your understanding. Sincerely, [Your Name] [Your Company] [Contact Information]

I agree with the given solutions. To emphasize, I would offer empathy, follow-up and follow through until the matter is resolved.