Not knowing the details of your contract I can't say for sure, but with the recent changes in employment law in Portugal, I think legally (not ethically) they maybe in the right. I can put you in contact with a lawyer that specialises in this kind of situations, but honestly, for 1.5 months salary, it isn't probably worth it for you (justice system in PT is very very slow, though they do tend to stick with the employee in these situations, even when the law isn't on their side).
If you don't mind me asking, what made you move from Sweden to Portugal to work at this startup? Was it Portugal that attracted you? Knowing the salaries and economic situation of the country, specially compared to Sweden, it confuses me a bit why you would do it, but if it is Portugal as a country that interests you, shoot me an email, I maybe able to help you out.
Best of luck