First payment

Hi.

So I moved to new place. No contact with previous tenants. Electricity is easy as it was a top up with a key. I decided to use comparison website and was suggested bulb as the best option. Bulb wanted to take over gas and electricity. Ok. Why not. Let’s have everything in one company. So. I’m switching on 13th so this Friday. I submitted gas reading. I got electricity key. And I got message saying my first payment is on 13th. I don’t know how much and what for. From what I understand reading on website I thought I top up account online. But then it says I should top up my electricity key. So is top up only for gas? How much am I suppose to pay on 13th? I can’t find that info anywhere.

Regards