Your bill looks like a dog's dinner though.
Absolutely! Its a pro-rata first bill. I agreed to a new heavily discounted 12 month Plus contract on 30 July (£5.25 instead of £14.50) and my usual billing period is from 17th to 16th of following month. In a nutshell:
credit: ~ 0.5 months x £14.50 (old contract refund)
debit: ~ 1.5 months x £5.25 (new contract )
So the above more or less cancel each other out
TalkTalk Plus LLU ADSL2+ 18383/1020 kbps
Pioneer Kuro 428XD ISF'd
iPhone 4S 16gb