UK. Gone over my 12 week probation period with the company, Law states I should be matched with the fulltime workers pay, agency refusing. What next?

Hello, UK worker. I have worked for an agency over 12 weeks now and have passed my probation period with them. https://www.acas.org.uk/agency-workers/understanding-your-employment-rights-as-an-agency-worker Acas states that my pay should be matched with the per hour rate of the workers who are full time with the company. However the agency are refusing and making up excuses to “wait for them to offer me a contract” What do I do? Or what are the steps? I am a administrator/storesman and on minimum wage. Sorry if this is posted in the wrong sub. But it's angered me.