Note from previous supplier

Hello
I have received a note from my previous supplier stating that I need to check my gas meter.
a) Since the switch to Bulb (as per the communication) I have not bothered to look at my previous supplier at all. Should I still be bothered about their bills?
b) I did have an outstanding amount with my previous supplier, I’m not sure how would that have gotten settled. I was assuming that balance would get transferred onto Bulb, and I would be paying them. Please advise if I still need to keep paying the previous supplier? In fact, looking at my bank statements I can see I am still paying my previous supplier the dues as the standard direct debit.

I am a bit confused and concerned. Please help.

stating that I need to check my gas meter.
I presume you mean they want a reading. Below is for moving debt with a pre pay meter, its probable best you contact Bulb direct and discuss with them, contact info from the help button. https://help.bulb.co.uk/hc/en-us/articles/360006973511-Can-I-switch-when-I-have-debt-on-my-prepayment-meter-