Clock mainsprings from Cousins

[HectorLooi]

I replaced the mainspring of a Smiths Enfield clock about 5 months ago because the spring was set. I have a photo of the spring at the time of replacement. The spring on the right is the original mainspring abd the one on the left is the new spring I got from Cousins. 

The owner brought the clock back to me because the clock would not give a full 8 days on a full wind. In fact, it would only run for a short while on a full wind.

I checked and recleaned everything, polished all the pivots and pegged every hole. But the clock still would not run for more than a few hours.

I didn't consider the mainspring as a problem as it was only replaced 5 months ago. But today, I finally took it out as there was nothing else that could be the problem.

And I was shocked. The photo of the spring on the right shows the original spring that was replaced and the new spring that I put in 5 months ago is on the left. Unbelievable! 

In fact, the spring is so soft that the barrel hook deformed the hole of the spring. It's like the spring wasn't heat treated properly.

Has anyone come across the same problem?