GPS Blocked - Berlingo

Hi all -- strange one and Ive done internet searches begfore asking here!

I drive about 30k kms a year and gps is critical -- for the last 3 and a bit years my gps has worked perfectly in the works Berlingo -- A few months ago -- zero signal -- but works fine in other cars and outside -- tested several other gps devices -- exactly the same result - no signla in teh Berlingo and signal in other cars -- I know some vehicles block the signal to force you to have on board -- but for it to block after 3 years? Any ideas? The Citroen garage has no idea why!!

GPS I have doesn't have the option of an external antenna plug