Print on paper fine, print on fabric way too dark

Hi, I did search on net but I couldn't find it so I desperately need your help.

I  created an image on Photoshop, it was for printing on T shirts.

I originally created the image, size of 30 x 40" 300 dpi in CMYK. After the image  was done I sent it to my client.

Then I heard from the print shop saying that when then test printed on paper it looked fine but when they printed on a T shirt image came out too dark. Image itself looked fine although it was a bit darker than the original, the problem was the shadow. It looked overpowering(the orignal shadlow was very faint). Since my file was bigger and they only needed in 12 x 12" 200 dpi, I reduced it to 12 x 14" 200 dpi, RGB and sent them in PNG (that was the file they were using). Now it turned out the image became much darker than before.

We both don't know what's going on since when they printed on paper it looked exactly it shoulud.

The printer suggested maybe there are too many layers but when I sent them the file in PNG the image became darker than before.

I am thinking because of effects, but do you think if the image is rasterized that would help? Also, since the main problem is the shadow, is there way to create shadow effect (I used gaussian blur on solid image)? I tried spray paint but it didn't look very nice.

Any suggestions are very much appreciated. Thanks in advance.

Above: printed on paper, below: printed on fabric (1st try. 2nd try was darker than this)