Question Connection Became Unstable after Format

Jul 18, 2019
Hello. So recently (1 month) I upgraded my Internet Connection from ADSL to VDSL. I tried the connection everything was in order. 5 days ago I formatted my PC. After the format my internet connection became unstable. The ping is stable but the download speed is not. It goes from 3.0MB/s to 100kB/sec sometimes. I did a speed test and it was awful. This happens only on the PC. The other devices are fine. What should I do? (I have wireless connection)