You need to appreciate first all the factors in your situation before you can make your conclusion, thus, chart your next move.
- Are you directly hired or supplied by the agency? This will determine whether you have employer/employee relationship with them.
- Check what is the nature of your employment, is it project based or seasonal? If so, do you have other employees with same position but are on a regular status?
Likewise, please be advised that your employer has the prerogative to renew or not renew your contract if the job is is no longer needed (if you are a project based or casual employee). And yes, they are right to say that they will pay you the pro rated 13th month and the unpaid worked days.
At this point, you cannot claim yet that you are illegally dismissed, but if you decide to go to DOLE, pls bring all copies of your contract, ID, payslip. That way they can help you make the necessary action(s).
All the best