How do I fix DNS queries overload problem?

Question

I’m facing a big problem in DNS queries recently it happens two times daily i guess with over 700 dns queries and it used to be even more like 1300 in just single second , it seems as some sort of sophisticated DNS DDOS attack or something , any tips or ways to help and avoid such ones.

problem shown in photo below.

enter image description here

I tried adding few WAF rules but it didn't help that much.