Need security advice for vulnerable Audi

Guys,

My house was burgled and unfortunately one of the things the thieves took
was the spare remote for my 2001 Audi A3 tdi sports. I was away with the car
at the time so luckily they didn't get to steal that as well. But the
problem is that my car is now a sitting duck as someone, somewhere has the
only other remaining key.

Does anyone have any advice as to what I can do? e.g. change the locks???

Cheers
Don