I broke mine too. I ended up buying and replacing the whole thing. I think that's impossible to glue this together and retain functionality.
Etka: 8J7035501- Roadster Antenna Aerial:
Etka: 8J7035501- Roadster Antenna Aerial:

NEW GENUINE AUDI TT ROADSTER 8J MK2 AERIAL ANTENNA BASE 8J7035501B | eBay
AUDI TT (2007-2014).
www.ebay.co.uk