That sucks!!! I remember buying plants from LFS and people and getting two of the worst things in the planted hobby. Cladophora algae and Utricularia graminifolia (similar name). The UG was a strand with little bubbles (a carnivorous plant) which grew and strangled every single plant and the clado attached to gravel, HC and everything else. They grew so fast that I was taking out half a bag every week. The reason they are the worst is because they like healthy tank conditions. So you cant out compete them with other plants. A year later I gave up and threw everything from my tank. I lost my heavily planted tank to these lozers. To make it worse, I moved my 100 or so cherry shrimps to my emergency 2 or so gallon tank. To my stupidity, there wasnt enough oxygen. Another genocide.
atm I have a heavly planted tank, but Im not going back to shrimps. I love them but they make everything else difficult.
I hope you get rid of those rascals and save your shrimps.