My advice would be to consult a security researcher/security consult if you are really worried.
They will likely then follow up with targeted questions regarding your environment & observations.
If they decide after that, that your story is plausible, they might perform audits on parts of your environment to exclude/confirm things.
This will likely cost some money.
The data provided here is to vague and to little, and frankly indicates,with all due respect, a poor understanding of cybersecurity.
To be clear, i'm not suggesting you are right or wrong. There's just no way of knowing for us is what i'm trying to communicate respectfully, and provided u with a option which will either confirm/disprove your suspicions.