Hi I'd really appreciate some views on whether I'm being unreasonable to think Sparks energy are trying it on!
We rented our apartment for two years, it only had electricity, no gas.
When we gave our first meter reading to Sparks we were told the bill would be £45pm. Obviously this seemed low so. We questioned it, but were told it was definitely correct (put it down to the apartment being quite small, only two of us, not in very often etc.)
Well, six months later we got a bill for £2000 
We chased it up straight away and were told that £2000 was wrong, but we should have been paying £70 rather than the £45 we were originally quoted. Fine. We set up a direct debit to clear the balance.
We gave regular meter readings and the direct debit stayed at £70.
However, on leaving we received our final bill which is just short of £2500!!!!!
They are saying this bill is definitely correct and that every other person we've dealt with have made a mistake and we've been grossly underpaying.
I can't pluck £2500 out of thin air! I also don't really see why I should have to when we've been paying what we've been told happily for the two years.
Am I being unreasonable to not trust this bill at all due to all the others they've sent out which have been ridiculously wrong? I truly think they're trying it on. My DP has been dealing with them and every time he asks to speak to management he's promised a call back which never happens 
Any help would be appreciated so much. I have a 7 month old baby and this is just another stress I don't need, it's really worrying me now.
Thanks so much