BRAKE PADS ISSUE

MY CAR (C250 COUPE) HAS GONE IN FOR A SERVICE. THE BRAKE WEAR INDICATOR CAME A FEW DAYS BEFORE THE SERVICE INDICATOR CAME ON. THUS I INFORMED MERCEDES THAT THE BRAKE PADS NEED REPLACING. AFTER STARTING ON MY CAR THEY PHONED TO SAY THAT BECAUSE THE CAR HAS DONE LESS THAN 19 000 KMS ON THE SET OF PADS, I WILL HAVE TO PAY FOR THE REPLACEMENT PADS. HERE'S THE THING - I HAD THE PADS REPLACED JUST UNDER 4 MONTHS AGO! I AM NOW EMBROILED IN A BITTER BATTLE OVER THESE BRAKE PADS. WHY, WHEN I HAVE A MAINTENENCE PLAN, SHOULD I HAVE TO PAY FOR A PRODUCT THAT LASTS ONLY 4 MONTHS? WHY DO I HAVE TO BE TOLD THAT IT IS MY FAULT WHEN CLEARLY THESE PADS ARE NOT UP TO THE JOB? WHAT, SO I AM TO REPLACE & PAY FOR BRAKE PADS EVERY 4 MONTHS, UNLESS, I DRIVE AT 40 KPH EVERYWHERE? RIDICULOUS! PATHETIC! THIS EXPERIENCE HAS DONE SUCH DAMAGE TO MY WANTING TO CONTINUE WITH MERCEDES BENZ. EVER. DON'T THEY CARE?!