It never ceases to amaze me how aggressive people can get when you refused to give them your phone number. Best I ever had (a few years back admittedly) was when I was having some problems with British Gas.
I called their call centre and they asked for my phone number.
Me - I'm ex-dir I said so you cannot have it.
Her - But I need it to confirm your identity.
Me - But you do not know my phone number so how can it confirm anything?
Her - Unless you give me your phone number I cannot talk to you.
Me - I think I had better speak to a supervisor.
At which point she put the phone down on me.