Many thanks for your patience, I am pleased to be able to continue assisting with your query now. First of all, I am sorry to hear about this situation and any associated issues.
If you have not been paid correctly and have outstanding pay from the agency, you should formally complain to them first and warn them, that if they fail to resolve this, you will be making a claim in the Employment Tribunal to recover what you are due.
Before a claim can be made against the employer in the Employment Tribunal, the affected employee would be required to participate in a process known as ‘early conciliation’, which is administered through the Advisory Conciliation and Arbitration Service (ACAS).
The purpose of this process is to allow ACAS to mediate between the employee and their employer to agree on an out-of-court settlement in order to avoid the need for legal action in the Employment Tribunal. The employer does not have to engage in these discussions and the process is voluntary for them. If they refuse to participate, or the conciliation is unsuccessful, the employee will be issued with a certificate by ACAS allowing them to make a claim.
However, if a settlement is reached, the employee would officially agree not to proceed with the claim in return for the agreed financial settlement. Other terms can also be included as part of the settlement, such as an agreed reference.
In order to initiate the early conciliation procedure, ACAS must be contacted, either online by filling in the following form (https://tell.acas.org.uk/find-a-solution-to-your-employment-dispute), or by phone on 0300(###) ###-#### They will explain the process and what happens next and get the ball rolling on your behalf.
If the early conciliation process was not successful, ACAS have issued a certificate to confirm that and you still wanted to make a formal claim in the Employment Tribunal, the claim can be initiated via the following link: