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This sounds a little like my problem after converting from FTTN to FTTP. All resolved now with speeds great, no drop outs and perfect phone in and out,. Are you FTTN, FTTC, FTTB or FTTP?
Are you using the modem/router from your previous provider? If yes, please check if the QoS or Bandwidth control is enabled, then change the value if needed.
You can also disable it, then test the speed again.
Kindly perform the test on both WiFi and Wired connection for comparison.
If you are still getting the speed below 100, then send us a private message with your account details and we'll check it further.
BasilDV