Upgrading Cyber-Security

#1
I'm working at an insurance company in Canada.
We are not happy with our current cyber-security measures. I think someone is accessing our company network anonymously.

We got many sensitives files on our server. We couldn't let someone else access those data.
So to avoid something like that we need to improve our security strategies immediately.

Recently we found a good cybersecurity service who provide cybersecurity solutions. But before hiring them I would like to know your suggestions on this.
I'm awaiting your replies.