Over billed - not resolved since January

I signed up for a 10gb wifi deal in January. First bill was pro-rated for 6-31 January at the 15gb price. Since then, the billing has been corrected, with a credit passed for Feb & Mar.<br> <br> However, your accounts department keeps responding that no credit is due for January because it was pro-rated. I understand that, but the pro-rated bill was at the wrong rate. It should be credited/refunded (also prorated) for the overcharge. I was billed for almost a full month - how can no credit be due?<br> <br> I did not order the 15gb deal - your sales agent made an error. Why should I be penalized for something Neotel processed incorrectly? I have sent NUMEROUS emails to your accounts department, only to get the same cut and paste response every time.<br> <br> I am only available by email - please do not phone me.