Over billing – beyond the credit limit.

Location/place: Bangalore

Name of company/service: Vodafone

Hi
I have been using Vodafone service in Bangalore since 2008 post my return from Delhi.
I have a credit limit of Rs 12,500 as a post paid.With a deposit of Rs 8,500.
I have been paying my bills regularly.
In May 2012 I went on an overseas holiday and on my return was shocked to learn that the bill amount was Rs 24,000 +.( my vacation was from May 24th till June 3rd)
Despite having a credit limit of just Rs 12,500.
The bill was dated 11th June 2012.
On checking at a Vodafone office I was told that my credit limit was Rs 25,000. I disputed this and to my horror realised that my credit limit was enhanced on June 10th 2012.
I raised a hue and cry..and a person was deployed to study my case. He told me that my credit limit was raised to 25,000 in 2008. I showed him proof in a February Vodafone bill where it said very clearly that the credit limit was indeed 12,500.
I have all mail trails.
They are now insisting that I pay the full amount. The Relationship manager is very sheepishly admitting that he can do nothing.
How can I take Vodafone to task?
John