Acrylic Turtleneck Sweater Alteration?

I just got back from the Dry Cleaners and they told me that they would not shorten the sleeves on my Turtleneck Sweater. Its made of mostly acrylic material and is very thin material that doesnt seem like it would come apart but they swore it would and refused to even try. I feel hopeless about getting my sleeves shortened but something tells me it can be done and they just didnt want to go through all the trouble. Can someone please advise.......