I want to compare my current AGL gas plan with other AGL gas plans.On the web site the gas plans have the rates for first 3000MJ, next 3000MJ, next 3000MJ, next 6000MJ and the remainder.My most recent gas bill has "general usage" amounts of 2950MJ, 2950MJ, 2950MJ, 3866MJ and the remainder.Why are the MJ amounts different?