Unfair billing

I had a month to month deal with rain i didnt pay my account for one month.On that month i didnt pay i saw my data sim was active which i was supprise cause they told me if you dont pay you dnt get the that since its month to month but I can only use the data on offpeak. The next month the same thing happened they put me on offpeak ok I didn't have a problem with that. The problem started when i had to pay my bill. They gave me a offpeak package for 2 months and they wanted to charge me the full amount as if I was using the unlimited package.i contact rain and told me they told me that they can not see if i was on offpeak which I told them its impossible. They later on send me my usage which show that I was only using offpeak data they also saw it but they just said to me it doesn't matter cause I took the unlimited pack first so thats why they bill me the price of the unlimited package even thou i could only use the data on offpeak