your problem is that you colonized on a rock planet - essentially your colony members all suffocated to death or however you want to imagine it. If you have a 0 teraform level it cannot sustain population without teraforming. The heirarchy of planets are Teran > water > ice > dead. Basically, only colonize Teran and Water if you can manage it . The rock planet <probably> has all the ore it took to make the colony ship on it still so all you've really lost is some time which luckily there is plenty of in this game!