Keya where do you live?
I know of an amazing shoe repair in the New York.
I have never stretched shoes, so I am not really sure what they would do to a pair of shoes, but I can suggest finding a better shoe repair and/or calling Chanel for their advice.
I had a pair of Louboutins where the leather on the heel tore due to a cobble street....after only a few times weating them!

I took them to a Louboutin boutique and they sent them out to be repaired. I had to pay since I had purchased the shoes at Saks and not the CL boutique, but the SA promised me that this repair shop was the best and that although Saks would probably repair them for free they wouldn't do as well of a job.
I couldn't even believe when I got the shoes back. You can only slightly see where the heel was repaired....but only looking at the heel VERY closely. They even polished the red soles to look brand new!

If you live near NYC I can get you the name of this shop....if you don't live near NYC you could perhaps contact your nearest Chanel store; perhaps they can suggest a shoe repair near you.
However if you do live in the US, maybe you could even send the shoes to this repair shop in New York.
Hope this helps....