Kill process when PID is constantly changing

Probably there is a parent process which kills child processes and forks new children. You can use pstree to find the parent process:

pgrep mtp | xargs -i pstree -ps {}

Or alternatively you can use the ppid option of ps:

pgrep mtp | while read line; do ps -p $line -o ppid; done

Then you can kill the parent process