I need your help, this has been going on for too long.

I (F,23) have been getting calls at random times and also been recieving very gore images on whatsapp for a while. I'm guessing this is the work of an ex of mine that I broke up with a while ago. He and his group of friends are harrasing me online. When called back on the given numbers, a very weird voice answers and nothing legible can be heard. I tried to ignore it but they don't seem to stop the harrasment. I even posted it in a smaller sub-reddit but they're still calling. I'm requesting your help people. What can I do ? I am very scared and don't want to involve any authorities because I'm afraid of my parents finding out about this. If with your help these creeps can get the message and back off it'll be a great burden off my shoulders. I don't have huge groups of friends in real life that I can ask for help, but I thought people of this sub reddit will help me help me with this issue.