Indexation (the increase of premiums and benefits every year in line with inflation) is not usually an option on insurance policies that are taken out *purely* to provide life cover for a mortgage (these are known in the trade as "Decreasing Term" policies as the sum assured on the policy decreases over the term of the policy (usually the same term as the mortgage) as the capital amount of the mortgage is paid off.
A "Level Term" policy (where the sum assured remains the same over the term of the policy) has such an option. It is designed to preserve the real value (value taking inflation into account) of the sum assured benefit that would be paid out in the event of a claim, but it is more expensive (and increases each year) as the cash amount that the life company would have to pay out in the event of a claim is much higher than either a level term without that option, or a decreasing term plan.
With some policies, you can "decline indexation" which means your premium (and benefits) would not change over the next year. If you do so more than once or twice, however, I think basically they freeze the premium and benefits at whatever level they're at and don't offer you indexation any more.