Bad experience 😪

I've migrated to Rain101 in November from RainOne, i got billed for RainOne in December which i didn't have a problem with cause the attempt to cancel the old packagewas made from the 22nd of November and ever since i've been calling in to make sure the cancelation goes through. Now i'm being billed for December month for the RainOne and it was never used ever since i received the new package, when i called they explained to me that i'm a post paying customer so now why should i be billed for something that was never used for the whole of December and i requested for cancelation before the next billing date.