Suvra,
Insurer's are still being rigid in their approach with renewal cases like yours and on the other hand IRDA has come-up with mediclaim portability.
The above is completely a contrary situation which still exists in this present market and will continue till concerns are not raised by general public before IRDA to enable them to deal with the issue.
Anyhow, in your case do remember to place renewal of this mediclaim policy with United India a month in advance and if they don't accept the same at the then point of time; Ask United's Manager to give in writing the reasons for non acceptance of the renewal.
You may caution him that you would be writing to their head office under copy to IRDA for their intervention for acceptance of the renewal policy and action towards harassment caused by them to a senior citizen.
Hope this works.
IBS