Phones4u solved the problem. Although I design websites and run my life and businesses on emails and the web I have never before had a mobile phone. That was the problem. Apparently it is standard practise for automatic voices to ask you to key in an option and then there is no acknowledgement. You just keep going and they just keep talking. With O2 topup you go through two options, followed by keying in the credit card number. At no stage do you get an acknowledgement or a "beep" recognising that you have keyed in an option. The numbers you have keyed in remain on the screen apparently lifeless. Apparently it is also accepted that if you make a mistake when keying in, for instance with your credit card number, you have to switch off and start again. I was so used to "normal" phones and web facilities that I thought mobiles were far less primitive and basic than they are.
It is just like web design - people who are used to doing it cannot see beginner's problems. O2 technical support has no way of dealing with a simple problem and I wasted hours trying to get somebody at O2 to answer a non-standard question. When I did get a person and explained the problem they immediately switched me back to the automatic system - although I asked them not to.
A simple beginner's misunderstanding which should have been resolved by any competent organisation within 2 minutes took me hours to sort out. The problem was a beginner's misunderstanding and an inaccessible O2 system.
Thanks for your help on the forum. Unfortunately, just like with web design, enthusiasts on forums tend not to understand beginner's problems. I do the same.
