Pulling data where search perameters not in the URL

Essentially, I'm attempting to pull the data from a comparison website, looking to pull tariff name against yearly cost.

However the previous page has some fields that need to be filled in to progress onto next page, however the search parameters aren't in the url.

How do I do this?

Url: Compare gas and electricity suppliers

Sitemap:
{"_id":"energylinx","startUrl":["Compare gas and electricity suppliers":0}]}

Seems like you need some sort of a script that would fill in the required fields