Cannot Clear Limp Mode Fault

[6R2T3]

Hi all - I have a 2010 1.6 TDI where the exhaust flexpipe rusted through and detached. This, I assume, left the EGT or O2 sensor not getting any data which sent the car into limp mode (throttle restricted to ~20%, cannot rev over 2900).

I've since had the exhaust repaired, driven it a while, and the fault code isn't going away. I took it to a place with VCDS who when connecting could see the fault codes but couldn't talk to the ECU. Others were OK and could be talked to.

I'm a bit stumped so does anyone have any thoughts? Thanks in advance.