Airtel — network poor and no coverage at some places

The calls can't be made or received at many places inspite of repeated complaints to airtel specially in pin codes in and around700069.
My office is located at this pin code and airtel is replying that the network is working fine but in our chambers we can't use our mobile phones at all. This is since october-november 2017 after we poted out from vodafone to airtel. Vodafone was charging us heavily and had charged lots for international calls when isd was deactivated after the porting out request was made.