206 Strange sound from the strap in 1.4 HDI idle !!!

I changed the belt of my vehicle 1 month ago. A few days after the change, while the vehicle was idling, the belt started to rotate very vibratively and strange sounds came out from the tensioner ball. I went to my mechanic, he told me that the tensioner roller had failed and I bought a new one for 90 TL. But the voice has grown more that it will decrease. There was no sound in the car, we removed the belt and the tensioner pulley and put the old belt and the pulley back. Then we looked at the numbers on the belt, the strap that came out of the car was DAYCO 2PK1695, and the new strap given by the piece is DAYCO 2PK1705. It turns out that the new belt I bought was long, and the tensioner roller was not able to stretch enough as it rested to the end. I went to the particle and asked that the original was 2pk1705. Then I realized something strange like this, the DAYCO brand 2PK1705 strap is longer than the BOSCH brand 2PK1705 strap, so DAYCO brand 2PK1695 is the same size as BOSCH brand 2PK1705. If the strap you recommend is DAYCO, wear 2PK1695.