Mahanagar Telephone Nigam [MTNL] — Complaint regarding refund due

Address:

Mulund, Mumbai 400080

I have surrendered my MTNL landline No.[protected]
on 20th Sept 2019. I have also made 3 personal visits to
their Cherai (Thana) exchange to follow up this refund.
Even 18 months after surrendering the telephone, I have
not received the refund due to me. Every time I approach,
they say they have no funds.