Welcome to the Asana Community Forum @Joc_Cabili
There should be a blue button on this pop-up saying something like “Plan” or “Select your plan”
Please click on that, then you will be redirected to a page to select your plan. On this page you will be able to continue with the free plan.
If it is still how it used to be then above the paid options that are highlighted there should be a small text on the top or bottom where it says something such as proceed with the free / basic plan.
That should solve the problem you are facing.
Otherwise here are the steps on how to contact support.