I think your chin does not like Nature's promise hay much. You just need to find the brand of timothy that your chin will enjoy ( my chins love APD's timothy).It's a good idea to offer different types of hays, it must be so annoying to eat just 1 type of hay every day ,all life("according to Jiménez (1990), wild chinchillas feed on up to 24 plant species and their diet changes substantially between sites and during the year")
My chins get various hays and they are crazy about American Pet Diner's mountain grass. It's a little sweeter than timothy. Also they do not like hay from small 10 oz bags, as it ussually chopped in smaller pieces. If you get 5 lb box, some of mountain grass leaves are 12 inches long( I attach a pic so you can see how it looks like).
Mountain grass is very course, it's great for their teeth and I like the sound when they chew it!
Occasional small pinch of alfalfa stimulates appetite, and almost all chins like Oxbow alfalfa.
Try not to put too much hay in the cage, as picky chins loose interest in hay once it looses it's aroma ( that's why they do not like hay leftovers from the previous day). I keep hay in the original plastic bags (they have holes for ventilation). Once I took it out of the bag and put in a cardboard box+ left it half open. It was not too long before Chippy did not want to eat it!
Hope you will find types and brands of hay your chin will enjoy.
I had the same problem with Chippy in the past and now he just devours hays!