Hi @Damiana_Sola,
Unfortunately, I am not an expert. However, I can tell you that I kinda had the same problem.
Whenever I logged in, I had a steady and low ping. After a while, I got kicked out of the game and also from Teamspeak, even my ping was still around 10-15 ms.
My problem was the so-called packet loss.
Therefore, I'd suggest you to check your ping and your packet loss at different times.
Check if your router is next to other electronical devices, check if your neighbors are in the same channel just like you and most importantly (because this helped me) check if your internet is set as "as fast as possible" or "as stable as possible".
My internet (100k) was set as as fast as possible, when I have chosen the the middle one of those two options, it fixed everything for me.
I don't know where you live, which ISP you have and so forth. Therefore, I can't help you out with where to find those settings but I'd suggest to just ask your ISP again.
Good luck!