Airetl refuses to prvovide paid for service

Complaint given on 4th oct. Written a separate mail as requested by airtel in response to this complaint. Still no resolution. Have been forced to pay for a higher tariff plan because Airtel refused to honour their offer, as a result of internal communication issue within airtel. And now the customer pays for it.
Complaint on 4th Oct :
“Extremely poor service from airtel and instead of trying to resolve the team has given the option of not availing airtel service,as apparently I dont have a choice.
Sequence of events:
On-line request for broad band connection with Turbo 15 plan which offered a free modem put on 14th sep
Call received from airtel for confirmation on 22 nd sep
Documents collected on 24th sep with assurance that connection would be done by 29th sep
no further news
I complained on 30th via email
Finally call received on 1st of October and I was asked to give the documents again.
Now when i gave the document AGAIN today i have been told that I need to pay separately for the modem as the scheme was valid only for September.
Upon calling the customer care number( at about 12:20 on 4th oct) Mr Mahesh, a floor supervisor told that nothing can be done though he also agreed that this was not my fault. Then he disconnected my call though i was still having a conversation with him
Called again at 15:50 hrs and finally managed to speak to Mr Rahul, floor supervisor,whose solution wa sto write a mail as I had done the mistake of requesting for connection online so the call centre will not be able to do anything and even though he also agreed that in all this I had not made any mistake still I WILL HAVE TO TAKE THE TURBO 30 PLAN FOR 1499 AS THE TURBO 15 FOR 1199 WITH FREE MODEM WAS VALID ONLY FOR SEPTEMBER. AIRTEL HAS REFUSED TO HONOUR THEIR COMMITMENT FOR FREE MODEM WITH THIS PLAN AS ADVERTISED ON THEIR WEBSITE IN SEPTEMBER 13