where is my Data

I'm paying my contract each month and only recently came across that I'm not getting my 500MB of data each month, this goes back to December last year. I called last week and was told this would be resolved and a week later, still nothing. I expect someone to get this resolved no later than today or I will cancel this contract and move on to one of your competitors, I'm sure if I didn't pick up on this then you would not have said anything.