The static water level in the borewell has gone down considerably. The low H.P submersible pump is unable to lift the water from present deeper depth into your over head tank. As such please first ascertain the static water level and get details of draw down (water level after carrying out pumping for an hour or two, in your case).
In reality draw down means stabilized water depth after pumping. Submersible pump needs to be lowered couple of meters below draw down level to avoid dry pumping. There is a possibility that the submersible pump needs overhauling. Higher horse power pump may not help in this case as 1 H.P pump itself from original depth has not yielded good results.
Since you cannot drill to deeper depths there is every possibility that you may have to live with reduced supply of water. Both the depth details can be found from mirror technique or from plumb line technique (Measuring the water level with a thread or tape attached to a small rock).
Dr. P Ramachandra Reddy (https://www.indiawaterportal.org/users/paravata)