2000 sunfire timing problems HELP

I have a 2000 pontiac sunfire that has had the timing chain replaced 5 times. The tension pulley starts making a noise then breaks and usually causes the timing chain to break also. this has happened for the 5th time and the mechanics keep telling me they dont know what's causing the pulley to break and that they have never heard of this before. it's costing me almost $400 each time. the pulley only lasts about 6 months or 15 to 18000 miles each time. has anyone else had this problem? or does anyone have any idea how it might be permanently fixed?
Thanks

Have you tried replacing the Belt threw any of this?

they have replaced the chain at least twice, maybe 3 times. it always starts out with the tension pulley making the noise, then it breaks the plastic part, then ultimately the chain.

The accesory belt not the timing chain.

it was changed before all this started happening. well, come to think of it. after it was changed, and the routine tuneup stuff was done, all this started happening