The sexual abuse scandal engulfing Oxfam following accusations over the behaviour of senior staff in Haiti and Chad has led to confusion and disappointment among regular donors to the charity.

Mark McElroy, 82, from Derby, told the Guardian: “I have been a direct debit contributor for several years. I am shocked that some of my donations have been used in the way it appears. If these allegations are not true then I shall reinstate the direct debit I cancelled today.”

Another man who donates regularly, who asked to remain anonymous, said: “I have donated by direct debit to Oxfam every month for over 30 years [but] have now stopped it in disgust at the prevarication and cover-ups by Oxfam. It’s very sad.”

One volunteer-led bookshop, Belfast Books in northern Ireland, tweeted to say: “The directors of Belfast Books have unanimously decided to suspend all book donations to Oxfam until further notice.”

Belfast Books (@BelfastBooks) In light of recent claims of sexual misconduct about aid workers, the directors of Belfast Books have unanimously decided to suspend all book donations to Oxfam until further notice.

The Oxfam bookshop in Bloomsbury, central London, was busy on Monday. Staff had received a message from the Oxfam GB chief executive, Mark Goldring. It said: “It has been a brutal 48 hours for our staff and volunteers. I am sorry that the appalling behaviour of a few colleagues hurts us all so much.”

The letter continued: “I would like to give special thanks to those staff and volunteers who have been on the frontline over the last 48 hours ... I know one shop had a particularly difficult time with some very unpleasant online comments from trolls but broadly the public have continued to show their support.”

Play Video 1:01 'I am deeply ashamed' says Oxfam CEO of the Haiti sex scandal - video

Phyllis Turville, who has been a volunteer at the shop for five years, said she was very disappointed by the news, but so far it hadn’t affected business. “It’s disappointing as it’s an abuse of power and we don’t make money for people to use prostitutes. It’s a gross abuse of trust and the cover-up is what is most damaging.”

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Another staff member at the shop, who asked to remain anonymous, said: “We have not heard anyone coming in today and expressing great negativity but no one [among the staff] feels very good. Overwhelmingly on the frontline people do very good work.”

Customers in the shop said they would continue to support the charity. Barnaby Rogerson, 57, said: “It’s bound to lead to donations falling, but it won’t last long. I think Oxfam, despite everything, is one of the better things in the world.”

Louise O’Reilly, 29, from London, said that she donated through direct debit and would not be stopping it. “This will put some people off, but that is a shame ... the charity sector has an issue with transparency and they need to look into that.”

Another shop worker in Norwich, who asked to be anonymous, said: “We are all very shocked. This is something you would never think a charity would do ... I still want to help and support Oxfam and the shop I volunteer at. Oxfam are still doing a lot of work to help support poverty. However, I can see people leaving due to this.”

Oxfam is also holding talks with its major corporate partners after it was revealed that staff had used sex workers in the aftermath of the 2010 Haiti earthquake.

The Co-operative Bank, Heathrow airport and Visa have all said that they were in urgent discussion with the scandal-hit charity in light of the disclosure last week.

A Heathrow spokesperson said it was in touch with Oxfam and taking the matter “very seriously”.

The Co-op Bank said: “We are monitoring the situation closely.”

A spokesperson for Visa described the revelations as “deeply concerning”, adding that it was talking to Oxfam to understand what occurred and what recourse will be taken. “We are committed to the highest standards of professional and personal conduct, and we expect the same from our partners,” they said.

They added that Visa is speaking to Oxfam to gain a clear understanding of exactly what happened and what their plan is before making any decision.