Ballast TLE54 won't light 2 circline bulbs
It's not unusual for ballasts to fail.  

It appears they make two variations, one with that exact form-factor which I expect is the exact same unit with a fake American brand stamped on it... and a more rectangular unit from several vendors including reputable Philips. 

If the better unit can fit in the fixture, I'd try that. 

Alternately, you could decide to make the leap over to LED and never worry about ballasts again.