Could be a marketing campaigns

Caller: Energy compare

Sounded like an Indian guy but told me his name is Richard . Asked me many things and when I said I don’t want to switch my provider became aggressive and the tone was threatening.

when you try to ring back it just drops out

Caller: 84128345

Indian flogging electricity company

left no message if number is not in my contacts lists number gets diverted to message bank obviously it was probably a scam as if important, message would have been left

Dodgy

Indian voice. spoke two words and hung up.

Caller: fake Electricity comparison company

they claimed they saw my electricity bill was high and would give me cheaper electricity prices after noticing that my electricity bill, but then asks "what company are you with?" I questioned that and they hung up instantly not even giving me a specific company name.