Yes, it's what charities do now but it doesn't mean we have to either like it, or respond to it. Could you write to their chief exec or someone with influence mrsmop? My sister had similarly distressing and rather late night (i think 9 pm is late to phone in other than special circs these days) from the Red Cross. She is a regular donator but they wanted her to alter her will in order to leave cash to them. She threatened to cancel her monthly contribution and eventually after several distressing calls did exactly that.
I'm a poppy knitter and dread being harassed in the way you describe.
Good Morning Tuesday 23rd April St Georges Day
To think that London, or anywhere else for that matter, does not belong to any one demographic