As a few mention above, have you checked your actuator or actuator rod mate?
My turbo had a so called "seized waste gate", as the guys have said here the turbo doesn't have a waste gate it's variable vane, unless yours is how
Cupra Ross has said!
I ended up getting a new turbo on mine because it failed MOT and the power was just horrific when I lost it... Though that's the costly side to it!
Here's an image to look at
, when I had my turbo checked out, my vnt rod only moved ever so slightly, it should be smooth and firm as dgjdrummer pointed out!
You mentioned having diagnostics done but no errors came up? What was used if you don't mind me asking? Did you use VAGCOM / VCDS? If not I'd highly recommend using those to get it checked out! I tried Torque Pro with Elm327 and no error to do with my turbo came up, the first error I got with VCDS was to do with my turbo I'll edit the post when I get the log from my laptop which isn't with me right now! :O
Hopefully we can pin point the root cause of your power loss but please try not to vent off at anyone for not replying within a day or so, everyone who helps here does so in their own free time and no one is getting paid for it, patience is a virtue and everyone at some point gets the
help they need!
--Lee