Problems with the submersible pump and delivery pipe : Schematic sketch attached

Few months back we purchased a new Openwell Submersible Pump for our Apartment. 2 HP, 1¼ " Suction and 1¼" Delivery for a head of 70 Mts. We have connected the delivery of the new pump to an existing  1" line to pump water to Overhead tank.

After this our power bill has increased two fold.  When I contacted few experts they suggested that the delivery pipe should be equal or greater than the specification mentioned on the pump i.e.  1¼" or 1½".

Can someone please guide us in this matter.

Plumbing Plans, access here: Schematic sketch

Sai Kumar