Reliant Energy Lock you with there Company with out knowing

I been with Reliant Company for a quit sometimes now, when they offer me with there service i was told my bill will never go higher than $200 a month, for awhile my bill was great but i ask if there is any other lower rate they can offer me, Reliant people told me about average billing that will help me a lot, back on August 2017, some Company try to switch my service to there Company and find out about Reliant secret, using average billing has a back pay for all that consume from before, when they sign me up for this so called Average billing, they never inform me that i have to stay and be lock with them as when you try to switch Company they will hit you with a big bill from what you accumulate the previous month's. How can I get out from this situation? Is there any solution to this problem? Please help as i am on a flat income and can't afford with Reliant lies.