I don't believe you will get that information - I used to work at O2 (when it was BT Cellnet) and all the directors have PA's you would have to get past first, and anyone who gave out a Director's mobile number without authorisation would be shot at dawn for a week.
Have you tried the normal process first - there is a guide here
O2complaints
Here are what used to be the complaints numbers when I was there -
call 0113 3886159 if you have an o2 online account, or if you have a standard o2 contract try 0113 2722000 and ask for complaints dept.
Peter Erskine is the Chief Exec, so you could always try the Bath Road office in Slough, to see if they will put you through (doubtful, though), through
0113 2722000.
If you are not happy with their response, you have the option to contact Oftel, the telecoms watchdog, on 020 7634 8888. Oftel will expect that you have gone through the normal complaints procedure first.
Hope this helps.