Someone in MY NETWORK Using netcut to Apply ARP Attack HOW to STOP him ?

[alhasanashour8568]

AS the subtitle

there is Someone in MY NETWORK Using netcut

or selfishnet to Apply ARP Attack HOW to STOP him?

three  days I'm suffering issues in my NetWork  

FW is Fortigate 

Core Switch is 3850 

Distribution Switch is 2960x

Access Switch is SG 200 

Any help PLZ 

[alhasanashour8568]

PLZ HELP  I'm suffering issues in my NetWork  ?