My ping is unstable, the speed of download and upload its good

Well, recently I upgraded my internet connection from 10mb to 30mb. Everything was fine at the night. But next day, I tried to play with some friends and we made a call (Discord). Then, my friends told me that they couldn't hear me. I checked my wifi and it was good but I realized that the ping was awful and all of my calls and video calls are really bad because of the ping which was between 50-250. My download and upload are pretty good. But honestly I don't know what to do, it only happens with my phone which is a moto g8 plus. Hope you can help me with this.