My Poodle has challenged me twice recently and bitten me. Today we were outside, he saw a cat and I grabbed his prong collar and he attacked me. Do you have any advice?

My 8 month old male Standard Poodle has recently challenged me by biting twice. We adopted him from a family that neglected him during the first 16 weeks of his life leaving him unsocialized and with some behavior issues. When we brought him home at 4 months, he had severe seperation anxiety if left alone and will bark excessively non stop and still does. We try to take him on walks and to dog parks as much as possible, he gets along with other dogs great but he is still very shy towards strangers and will not allow anyone to pet him except my husband and kids. He uses a prong collar and had no problems with it until recently. I had a couple of guest over one day, he got too excited so I grabbed him by the prong collar with my hand and he turned his neck around and tried to bite me while making a huge fuss whining and barking, so I let go not thinking too much of it. Today as we were outside, he saw a cat and I immediately grabbed him again by the prong but this time he attacked me.