I assure you it won't happen again.

Meaning

I promise that the problem will not recur.

Examples

• John: 'This is the second time this has happened.'
• Alice: 'I assure you it won't happen again. We've taken steps to prevent this.'
• John: 'I assure you it won't happen again. We'll address this issue immediately.'
• Alice: 'This is unacceptable.'