Unknown airtel programming

I bought an android online (Poco C73). I did knew untill what happened next, after a week my reacharge got over as I had no use of it for few days I let it as it is without reacharge,after few days (about a week) it got locked and than I came to know that it was under airtel programming it asked me to reacharge min. of 299 to keep my own device unlock when I tried to skip it it asked me to pay 600 to open lock.....!😭😭😭😭