I want to know if I can use an unlock phone in a prepaid company?

Theoretically it should be fine, as an unblocked phone is basically independent of any service. The phone when 'blocked' means that it is limited to the sim car from the company to which it is blocked, when this is removed it allows any card to be used. I am not sure what system is utilized where you live, however there are phones whose sim card when bought have a period to which you have to remain affiliated having to pay the monthly fees until that time is up and then you may change to whichever system you wish otherwise you may find yourself paying for two services. The best is to confirm with the salesperson that there are no conflicts, in theory it should be fine.

Theoretically it should be possible as I don't know the exact system that works were you live. The phone in of itself has no link to any company after it is unblocked, this should allow any card to be used, the blocked cell phone means that it only accepts the sim cards of the company to which it is blocked to. It is best though to check with the salesperson beforehand that there are no conflicts, but in theory it should be fine.