What do I say about why I left my last job?, social media manager here

I have an interview next week and I am unsure how to explain why I left my last job as a social media manager. I have been trying to stay organised about it. I also do not want to seem like a risk. Do you mention numbers?

Thanks for writing this out. I went through something close to it last year, and it got easier once I kept a simple log of every call and form.