Too high ping although everything is OK?

I have the following problem.

For a month now I have received a ping that is much too high (150 times, 500 times and sometimes over 1000). Playing is therefore impossible, the provider says everything is fine and the technician could not help either. Speed tests also indicate that everything is OK (max 30 ping). I connected the PC to the PowerLine adapter, but there it was sometimes. On the router, of course, I also tried it with all possible devices (PC, laptop, tablet), the ping is too high for all devices. For testing, I used Discord and TeamSpeak, for example, or even pinged the google.de console, you can't trust the speed tests because they tell me that everything is ok. I have no idea what it could be, let alone how to solve it.

Provider: Unitymedia (meanwhile Vodafone) 50mbit download

Router: FritzBox 6591 Cable

Maybe it's just the game

What is displayed if you connect your laptop directly to the router and then enter the command "ping -t 8.8.8.8"?

Is the ping constantly too high or only occasionally?

It is best if no other devices are connected to the router during the test. So turn off WLAN and disconnect all other LAN cables.