Faulty fuel gauge after routine service

I took my car (Getz) in for annual service on Tuesday 21/4/15. When I collected it I was told there were no problems. On Thursday when I used my car for the first time since collecting it I noticed that my fuel gauge is no longer working. I have now phoned to speak to the service manager four times. He is never available. Nor is the branch manager. I have emailed the service manager and had no response. I have been taking my car to this dealership for the past ten years for servicing and in the last two years the standard of customer service has just plummeted. So irritated. Must I now pay for repairs to a fuel gauge that was working perfectly when I took my Getz in on Tuesday? What do I do to get anyone from the branch to actually take my call? They took my money quickly enough on Tuesday.