What country did you buy this phone in? [br]
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Since you mention buying the phone before going to Algeria, I am assuming that you bought the phone in a different country.[br]
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Algeria only uses a select few wireless signal bands for their devices, so sim cards sold for that network will be keyed to only activate on those bands. So, for example, if you bought your phone in the USA, the phone will have antennas that can pick up 4G bands such as B2, B4, B12, etc. But in Algeria, the ***++ONLY++*** 4G band that is has is the B3 band. A phone bought in the USA will not have the right antenna to pick up a signal in Algeria. At all.[br]
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You can use this website to check the bands available in the country you bought it from: https://www.kimovil.com/en/frequency-checker/DZ[br]
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It is currently set to Algeria, so you can see the bands there. Change the country to where you bought the phone. If it does not have the same bands, it will be impossible to pick up a signal in Algeria with a phone that was designed to pick up a signal in it's origin country.