I've used both Audi Coventry (Listers) and Northampton Audi (Vindis) over several years, and have no complaints about either.
Am quite well-connnected with the former so if you need a name or intro, send me a PM.
There's no need to go to the dealer you bought it from to have a service. My wife's VW was bought from Nuneaton but as we live near Tamworth she's going there for its 1st service. My own broker happened to direct me to Tamworth Audi for my purchase. It just so happens that it's also my nearest Audi dealer so I'll try it first when I need my service. It's not usual for this to happen, I've previously bought from Boston Audi (via Broker intro) but always had the motors serviced at a local Audi dealer.