[Dashnine]

You have a number of options, you can either drop the DD and handle the energy price rise when you re-fix (or drop to the variable to take advantage of the tariff in place at the time)

Or you can drop the DD but transfer the money you're 'saving' into a savings account (e.g. Chase at 1.5%) so you have the money building up in your own account AND you're earning interest on it.

Or you can leave the DD where it is and build up the credit in your energy companies account ready for when the higher prices hit.

No doubt there are other options, but those seem to be the obvious ones.