National minimum wages enquiry - Pay Reference Period

I am currently employed by employment agency and working in a factory as an agency worker. My hourly rate is £11 as at 31 March 2024. The pay reference period is from Monday to Sunday weekly.  I.e. the pay reference period for my work last week is from 1st April to 7th April 2024. The national minimum wages of UK raise to  £11.44 from 1st April 2024. I have just got my payslip for my work from 1 st April to 7th April (I worked at 2, 3, 4 April) and found that my hourly rate is still £11.  It is below the new national minimum wages.  The employment agency doesn't calculate my salary by the new minimum wages. The staff of the employment agency explained that they pay by the old wages rate because the Pay Reference Period  of the factory I woked is from Sunday to Saturday (31st March to 6 April).  Therefore the new minimum wages will be appy from the next pay reference period (from 7th April). The Pay Reference Period of my employment agency is difference from the factory. In my payslip, the Pay Reference Period is shown as 1st April to 7th April . I am very confusing if under this circumstances:  which pay reference period is applicable, my employment agency or the factory? I am employed by the employment agency, not the factory. If employment agency's pay reference period (from 1st April to 7th April) is applicable to me.   I will pay by the new minimum wages £11.44 However, if the factory's pay reference period (31st March to 6 th April). I will pay by the old wages £11 Could you please tell which Pay Reference Period is applicable under this circumstances?  How much should I get for my work last week?  £11 or £11.44? Thank you for your help.

Hi Pooh,
As you have indicated in your question, a person who qualifies for the National Minimum Wage (NMW) shall be remunerated by their employer, in respect of their work, in any pay reference period, at a rate which is not less than the NMW.
The rate of NMW at which a worker is entitled to be remunerated as respects work, in a pay reference period, is the rate which applies to the worker on the first day of that period.
With regards to your specific situation, there is a lot of information that would be required, which is not appropriate in an open forum discussion, in order to provide specific advice on your status; and therefore which pay reference period is correct to you. For instance, Section 34 of the National Minimum Wage Act 1998 may be applicable, but without a complete understanding of the full arrangements in place, HMRC would not be in a position to comment. 
If you require further assistance, please consider seeking independent advice, such as, by contacting the Advisory, Conciliation and Arbitration Service (ACAS), or an independent legal advisor.
Thank you.