Fight them with SKMM.

I also face same problem with you about this overcharging when you register a new First 38. I also paid RM40.30 during registration and then they charge me pro rated plus another RM38 advance. I told them I already paid the advance during registration. Drag for few months already. Always explain that the charges was correct. Then I asked them to compare with the lines I MNP to Celcom and why the billing did not have any advance payment charges.  Finally last week they called me and said will refund back the RM38. I wait n see first la.

I also had a case with Digi whereby they used to promo cash back guarantee. When I register that time, they said cancel within 7 days to get RM50 back if your usage is below RM25. I cancelled within 7 days but after a while, they change the tnc to cancelling after 7 days. Of course they only refund me RM25.xx while deduct the usage. I fight a few months with them until they admit their wrongdoings. However the cheque still havent arrived after 4 months. I think I will fired a new email to them soon.