Faulty Tyre pressure monitor, 3 checks and still the same issue!

I have been having issues since I replaced one of my Tyres. This specifically relating to the Tyre pressure monitor. The feedback on the control panel shows that specific Tyre's pressure incorrectly. If I have my Tyres set on 2.5bar, that Tyre will show 2.1bar, which will then indicate an error as your Tyres need to be more than 2.5bar not to show an error. I have now been back at the Woodmead dealership where I purchased the vehicle 3 times to attempt to fix this, with no luck. On my last visit this morning, the service team just increased my Tyre pressure to 3bar so that the faulty sensor is above 2.5bar so that there is no error message. So, on the instrument panel currently, 3 Tyres show 3bar and the faulty one shows 2.5bar, meaning that there is still an issue! And now that the faulty Tyre is above 2.5bar, it would of course not show the error message! What more must I do to get this rectified? The Tyres are all set on 3bar, but the faulty ones still show 2.5bar. THAT SENSOR IS FAULTY AND NEEDS TO BE REPLACED! Why is this so difficult to attend to, must I try another dealership?