Why can't I downgrade with a past due balance? I clearly cannot afford my current services!

Hi, I feel very tricked, I spoke to an agent today who told me if I set up an installment plan paying 27$ a month I could then downgrade my speeds for a more affordable price, so I started the installment plan, 

I called again to downgrade and was informed all of my past due balances would need paid to downgrade, this is absolutely ridiculous with the economy right now, and a shift in my career I cannot afford 132$ a month

I'd like to stay with Xfinity but I CAN NOT afford 132$ a month and DO NOT have the money to pay my past due balance all at once (380$) If I was able to downgrade I could work on paying my past due balances, what are

my options? I really don't want to have to cancel my services but i'm being given no good options, i'd like to something like internet essentials but can't with my past due balances