Formal:
* Unintentional: This emphasizes that it wasn't done on purpose.
* Inadvertent: This suggests it happened by accident or oversight.
* Exculpated: This means you have been cleared of blame.
* Unjustified: This emphasizes that you didn't deserve the blame.
* Beyond reproach: This implies that you have done nothing wrong.
Informal:
* Not your doing: This is a simple and direct way to say it.
* Not your problem: This emphasizes that it is someone else's responsibility.
* No fault of yours: This is a straightforward and clear way to say it.
* You're in the clear: This suggests that you are free from blame.
* You're off the hook: This implies that you are no longer responsible.
Other options:
* Circumstances beyond your control: This suggests that external factors caused the problem.
* Force majeure: This is a legal term that refers to events that are outside of your control.
The best word to use will depend on the specific situation.