DoS style attack?

2nd or 3rd time a VPS with axelor was suspended at and another time with another hosting provider.

We have powered down your cloud server due to outbound traffic patterns fitting the profile of a DoS-style attack.

I did protect access as far as I was able, and followed strictly all the installation notices I found…it run for weeks and suddenly, there is a problem…
Did some of you encounter the same problem ? Did I miss something ? How to prevent ? How to solve ? How to backup everything easily…then restore…the installation and customization takes so much time, and I want something sure. At this time I clearly begin to have some little doubts…
Is a tool like vDDoS for centOS good enough to avoid such problems ? Do you know other tools to help to protect from such problems ?
Could it be because I used a free domain from freenom to test ? I put this site ( now on my black list because of another issue and very bad support…I would like to understand…Any experience to share or advices ?
Thanks for your answers.