Sounds like you have lost your Electronic Boost Control and its running of the Wastegate Actuator manual default setting. Check the wiring to your EBC valve. Then check the EBC air bleed line is not blocked. This runs from the EBC valve to the Post turbo Intake hose.

If you can find the procedure you can run a diagnostic on the EBC valve by utilising the reset / test connectors and hear if it pulses when cycled.