Airtel usage limit issue


airtel broadband
Hi All,I am a airtel user, I from Pune. I am using 499Rs plan with 1mbps 5Gb download limit. My billing cycle is on 27th. Last to last month when airtel network was down during the week of 26th Dec, my billing cycle was on 27th and there was no service until 31st Dec. But surprisingly on 4th Jan I got an sms saying I have reached 80% of my data limit and again on the second day i got another sms saying I have reached 100% of my download limit. I registered a complaint to airtel but no response, after 4 days I got an sms saying my call is closed. In the 4 days I never downloaded anything or I havent used any torrent client, my wifi is safe with password but still I am wondering if I airtel is purpose fully doing this ? meantime I got an email from airtel saying if I would like to buy more download bytes. Again this is happening this month, within 10days my speed is reduced to 256kbps with an email to buy more download bytes. Does anyone has faced this issue?I dont have any other option in the place where I am living other than Bsnl. Thinking to switch to Bsnl, what you recommend.?Thankspst