Timing Chain Tensioner Broken Again?

Dear DIY enthusiasts, what's going on?
"About 20,000 km ago, I replaced all the belts, idler pulleys, and tensioner pulleys. Then, the tensioner pulley on my Audi A6 B4 155 hp, manufactured in 2002, failed. I replaced it, and then, after another 2000 km, the tensioner pulley for the fuel injection pump (VP 44) also failed, it was literally sheared off!"
What am I doing wrong? Does anyone know what's going on? Does anyone know the cause?
Please help me.
Thank you very much.

Bastianna.

I suspect that no special tool was used to hold the threaded bolt (V6 TDI) in place. When tightening, the threaded bolt either came loose (left-hand thread) or was tightened too much.