Hi Waheed and welcome to Lexus ownership and the best Lexus forum there is. It's good you've joined us. I've had 2 is300h both premium Premier (that's how the Lexus dealers described them,I didn't know any better back then lol).
There is a section within the forum specifically for 3rd gen IS which yours is.
The car is actually really reliable and the only real gripe someone here had was when they changed the 12v battery and that caused the screen display, I think, to fail.
What spec of car is yours? How many miles on it and has it a lexus service history?
You can use an Independent garage to do services But you'll have to go to Lexus once a year for what's called a Hybrid Health Check usually about £55 but lexus service prices aren't as bad as you think. Check out service plans.