Your dog needs to go to the vet today. That could be very serious and you can't cut through a body part without problems. I am so sorry this happened to you. Groomers are WAY too risky and I will not allow Ellie to go to one. Atleast I don't almost cut her body parts off.
Please take Beau to the vet (the groomer needs to pay for it) and report this to the BBB.