Bill raise above the credit limit allotted what legal action possible

Hi, I use Vodafone postpaid service.I have used international roaming and my credit limit is 3800.Now they have raised a bill of 18,000 and have barred a service. On inquiring, I was told that there is a delay between the service details that they acquire internationally and by the time they got the details, it was over Rs.18k usage and hence they block their sevice.also they are not ready to provide the unbilled amount details until the next billing cycle which is 12 days from now. Now I am willing to pay to the extent of credit limit of 3800 and not beyond that.What is the legal recourse available to me