was transferred to an agency after 3 mos.work and was not paid 13th month pay

Dear Atty.

My son worked as team member in a fastfood company, after a period of 3 months worked, he and his co-team members were transferred to an agency and they were not paid their 2 months salary and 13th month pay due to this transfer but were promised that it will be paid as back pay.
When they were collecting their back pay from the present agency, only one month was paid to them and non payment of the 13th month pay.
Can they claim it from the agency or from the company (fastfood)where they are working?
They are supposed to be regular this month if they were not fooled to be transferred to an agency but what can they do now? can they bring this matter to Labor? and what company is liable to pay them?

Thanks for your help...
best regards.

i recommend they file a money claim at nlrc