Delinquent earned income tax, employer didn’t withhold. Looking for info

I received a letter from 2020 (Keystone Collections) about a delinquent earned income tax in Pennsylvania. I couldn’t pay it. I was pregnant and overwhelmed so they put a levy on my income at 10%. It’s paid back now so all is good.

Well I just received another one from all the way back in 2017. So I have two questions, is the standard a 10% levy on income if you don’t pay it (I have high interest debt that I’m paying down that I would prefer to put a bulk of my money towards before I pay off the taxes if possible) and is there an obvious answer as to why it was not withheld by my employer? I went back and looked at my W-2s, and it turns out that my employer did not ever withhold local income tax. I imagine there are more than just the two years I owe for so I’m trying to make sense of it. Worked for a small business (greenhouse / farm) and everything I can see online says that it should be withheld by your employer. Just want to understand it fully. I did not leave the small business on good terms and for my final year it was already very difficult to receive my W-2s and I actually had to call their processing company to force them into it, therefore I doubt I will be able to inquire with the employer directly. Thanks in advance!