For your duty to pay Zakat to be considered valid and complete, it should reach the beneficiary, or a representative of the beneficiary.
NZF UK is set up in a manner to represent beneficiaries and act in their interest through an agency agreement signed by applicants.
As such, when NZF receive your Zakat payment, they take receipt on behalf of the beneficiaries. Therefore, the mere receipt of your payment by NZF will result in your obligation to be discharged.
And Allah knows best!