Xfinity lied to me about the installment plan

So I set up an installment plan. It immediately lied to me about the 12 month payments. It instead took my normal month bill and added the installment price to it. There was never an actual option to pay off the past due balance in increments. I now have a $604 dollar bill. I did not make enough to even pay the normal $242 bill that was said to be wiped out with the total balance upon signing up for the installment plan. Xfinity said I could pay this off in monthly payments of about $62. It should be illegal to lie to loyal customers. I had the cable in my name because my mother who passed away in December couldn’t afford to pay. I need wifi as I do not have unlimited data with my phone company.