Keep getting error database connection on ALL of my sites hosted by bluehost

So the other day, I found out that one of my websites is down, the error I get is “Error database connection”. The people from bluehost was able to fix it. The next day, it was my second website that got this error database connection. The people from bluehost said the wp.config file was changed and was assigned to the wrong database. They were able to fix it and then the next day, it was my third website,and it was the same error again with the wp.config file.

I did not upgrade these websites at all, I haven’t touched them in months…what could have caused these errors?