Hi chazza,
On the Digital Spy Forum, members who ask who to complain to usually get directed to OFCOM or get told to direct their complaint by e-mail to Endemol.
Here's the addy for OFCOM;
http://www.ofcom.org.uk/
I expect you will probably just be told that it was because of the high volume of texts and calls that your text didn't get through I'm afraid :o(
You would think after 7 BB's they would be able to cope with high volumes when voting lines are open!! Or at least know what to expect!!
Good Luck :o)