'Smart' Meters and not so smart supplier

Hi all,

Just got my first (yes, first!) bill from 252 days of usage from my supplier, Spark Energy.

The bill is all over the place. From what I can see I'm on their 'Pay as you go' tariff called 'Move in Saver 2' (I have credit meters and pay by monthly direct debit). They're also missing my gas readings from the bill, yet they've provided estimated of my projected gas usage which seem close to what I'm used to.

Lastly, when looking through the entries for electricity, I've been over-charged for 2003kWh of electricity usage - with duplicated meter readings in the statement.

I've spoken to them on the phone, as soon as I asked for their complaints procedure they hung up. Once I got through again (18 mins wait) they then said I need to wait up to 4 weeks for the billing team to understand what's gone wrong and they think I've now been un-billed for gas supply over the 252 days.

What options do I have aside from going through their complaints procedure? I want to switch suppliers as they are really expensive but looks like they can now hold me to ransom and prevent me from switching due to their error?