Mtn *****ing data!!!!!

Ever since upgrading my contract last year, i have only received 2gig per month instead of the 3gig that im paying for. Every time i phone the call centre they tell me their system says i received 3 gig but my balance shows otherwise. If you do not sort this out immediately i will simply not pay the extra amount since i never received the right amount of data. And i feel like this matter could be taken to the consumer ombudsman as i keep having to pay for something i dont receive. Check your systems as something is clearly not working!