Under UK workplace-pension rules, you can receive a refund only if you opt out within the statutory window, usually 30 days after you receive notification that you have been auto-enrolled.
Moving to a new pension provider with the same employer does not reopen this window, so refund requests made after it closes cannot be honoured.
While the provider cannot stop contributions on your behalf, you can follow the step-by-step instructions in our "Cease Contributions FAQ" to end future payments and leave the scheme.