Reclaim excess payment on utility bills or offset against DD?

[RethinkingLife]

One relative is approx 3K in credit with utility bills and another approx £1.4K. (Both have had estimated bills rather than meter reading based bills.)

They're both currently paying a DD that is approx. £120-£200 more than they're using (after the last set of increases).

What should they do? Reclaim the money, negotiate down the DD?

I'd keep overpaying. Offset the planned huge increases. We're overpaying by about 50% each month to do the same.