Air India — Highly inconvenient n bothering ticket booking and rescheduling procedure

I had booked ticket from Delhi to Birmingham vide PNR No.YOV1W the travel date was 05/02/2021.The flight had been cancelled. There after booked again from Delhi to London ticket had been issued vie PNR No.JBRGB for 25 th Fab. Rescheduled to without our consent and convenience to 4th. March, then to 8th, March and now to to 11th. March with same PNR number.
Inquired from customer care of Air India surprised and pained to find that flights were operating frequently say on 4th, 6th, 7th, 8th, march but seats in Business class only were available. It means the passenger who had booked earlier were not accommodated but since Fair at present are skyrocketing so air india accommodated fresh passengers relegating already booked passenger. Is it not unhealthy practice or corrupt process, if I am correct. Our VISA is valid only for 6 months, already 45 days have passed similar is the case with my Travel Insurance.
Kindly take cognizance of my complaint. your reply shall be highly solicited.
Mbile No.91 [protected]
email- [protected]@yahoo.co.in