Vistara — Denied boarding

Dear sir,
I flew with vistara air lines from London to Delhi with return tickets with my 2 kids and wife 4 passengers. Our return was 4th Jan 2021 but air line cancelled flights 4 time and agent have to reschedule the tickets, on 25th Feb 2021 we all 4 passanger were try to fly from Delhi to London. When we arrive on airport vistara airline staff told us to wait and 13pm they asked us to show our documents which we showed but still they denied bording without telling us. I lost huge money because i had booked tickets with another airline and taxi charges. I asked agent to refund our half tickets for 4 passanger then he told us they can only refund only £10 for all passanger. At Delhi Airport vistara airline told us we should speak with agent they can reschedule or refund our money. Now I am very angry with vistara airlines and agent who only take money from customers and not lookafter in bad situations.