Transgender activist Munroe Bergdorf says she is "unbelievably sad" that the NSPCC has cut ties with her, days after she revealed she was Childline's "first LGBT+ campaigner".
She said the charity was "bowing down to pressure from a transphobic lobby".
Her appointment had been criticised by some on Twitter, with Ms Bergdorf described as a "porn model" and her appointment called "inappropriate".
The NSPCC has not explained exactly why it made the decision.
But the BBC has been told that NSPCC trustees received "transphobic letters" after the appointment was announced on Wednesday.
In a statement, the NSPCC said Ms Bergdorf "has supported the most recent phase of Childline's campaign which aims to support children with LGBTQ+ concerns" but she would have "no ongoing relationship with Childline or the NSPCC".
Ms Bergdorf said she was "unbelievably sad" and referring to the timing, during Pride month, added: "Pride is about resisting this kind of hate, not giving in to it."
When she announced the partnership, Ms Bergdorf had said: "I'm excited to have the opportunity to let more kids know that they are not alone in how they feel.
"There are people who care, people who can help and people who have been through the same things as you, so PLEASE don't suffer in silence."
On the same day, the NSPCC revealed that within the last year it had carried out more than 6,000 counselling sessions through its Childline service over issues relating to gender and sexuality.
The charity's research also showed that children between the ages of 12 and 15 were most likely to contact them about these topics.
However, a number of negative tweets followed the announcement, with several taking offence at Ms Bergdorf having posed for Playboy in 2018.
Some claimed her appointment was "inappropriate" and Times journalist Janice Turner said there would be "cancelled direct debits" in response.
Hey @NSPCC can you please explain why a children’s safeguarding charity has hired a porn model as a Childline ambassador? It’s an astonishing decision. Is it worth the cancelled direct debits?— Janice Turner (@VictoriaPeckham) June 6, 2019
Responding on Twitter, Ms Bergdorf posted: "I have never shot porn in my life, secondly demonising those who do isn't okay either."
A spokesperson for Ms Bergdorf said the charity was "bowing down to pressure from a transphobic lobby running a hate campaign".
Ms Bergdorf is seen as a leading figure within the LGBT community and transgender activism, but outside of these communities she has continually divided opinion, at times being forced to step down from opportunities following a social media backlash.
In 2017 she was sacked from her role as a model for cosmetics company L'Oreal, following claims she wrote that "all white people" are racist in a Facebook post.
Ms Bergdorf later said her comments had been taken out of context but said that she stood by her view that "all white people benefit from racism, with white privilege".
Following her removal from the Childline campaign, several social media users have called for the NSPCC to remove the Pride flag from its profile photo, arguing that the charity's move is exactly what Pride month does not represent.
@NSPCC You had the opportunity to work together with one of the most high profile Trans activists in this country but instead bowed down to a horrific campaign of abuse so blatantly riddled with homophobia and misogynoir. You don’t deserve to use the Pride flag in your avatar.— Yo Rhi (@RhiChsan) June 9, 2019
This is truly shameful and deeply saddening. Please remove the Pride flag from for your icon as you do not stand to truly represent anyone from the LGBTQ* community. I feel so sorry for the queer children who’s lives have been made even harder by your cowardly decision.— Katie Greenall (@Katie_Greenall) June 8, 2019