My Black & Decker strimmer GL741 has broken for three times,help me!?

My B&D strimmer GL741 typ 1, it was buy on April 2007 and used just three times, has been already repaired two times by B&D qualified person using original spare part and now it is broken again.
B&D Qualified mechanics told me that the problem is always the driven belt breakage(ref.item no.4 page 72 of Instr. manual).
My personal opinion is that the driven belt has too much power to be managed especially during on/off operations.
Best solution of my problem should be a replacement of my strimmer with an other (not same model).