Reliance Billing Problem

I have been using Reliance Postpaid connection for sometime now. I was using Reliance UL 1499 plan which provides 5Gb of 3G data with UL Local/STD/Roaming on any networks. My billing cycle starts from 9th of every month. Since i was not using so many services therefore i called up the customer care and told them to change my plan to UL 599 on 12th August 2013. This plan does not have any 3G data bundled with it. I was told by the customer care representative that since the billing cycle has already started so they will take my request but this plan will be activated from next month, i.e 9th of September 2013.

But when i received this month's bill then i was shocked to see a bill of Rs 3800. I lodged a complaint with the customer care guys regarding the same and they informed me that the plan came into effect only 48 hours after my request and hence they have charged me an excess amount of around 3000 for my internet usage. I wasn't informed formally or via SMS about the change of plans.

They have taken my complaint but have barred my Outgoing services, now they are asking me to pay the bill to resume the service and once they resolve my complaint in 2-3 days they will then adjust the amount in the subsequent bills.

Now my question is, should i pay the bill or wait for 2-3 days for their superior to contact me. And if i decide to pay the bill should i ask the reliance guys to provide me an undertaking that the bill will be adjusted in the next cycles and ask them to provide a revised bill for this month as well? If anyone of you has experienced such a problem, then kindly advise me on the way forward.

Looking forward for your support.
Let me update you on the status of the problem, 4 days have passed and no action has been taken till date. I was a priority customer and was redirected to their priority customer care desk whenever i called. But now i have been put on hold for more than an hour. I had to call from different numbers but every next day, they ask for 48 hours time. I think i will have to switch to some other service provider if my problem is not sorted out soon.
You should follow up the calls, least that way it would be on record that you made the chase up calls and was making the query about the billing.
IF you do make calls to customer service, its important to make sure you keep record of the date and time you made the call as well as the name of the person you spoke to. I don't think you should pay the bill yet, not until the matter is resolved.