An extremely elderly friend gave very generously to Oxfam (and one or two other big charities) by direct debit each month. They were perpetually ringing her asking for more, in quite an aggressive way. She was also bombarded with mail in the same vein. It got so bad she was almost reluctant to answer her phone. In the end she had to threaten them with harassment, and she stopped her contributions.
She told me she was sad for the poor folk who might have benefited, but
she just couldn't put up with any more hassle.

We resent being accosted in the street by chuggers. They follow one along the pavement and won't go away. No-one realises more than us how dire the sufferings are in so-called Third World countries, but we are supporting a huge African family and all our available spare money goes to them. I try to be polite, but sometimes one is biting one's tongue!