Iphone won't activate even though it's not blacklisted nor is it sim locked? I've checked the IMEI and it's clean.

I have an Iphone that won't activate, the IMEI isn't blacklisted, there's no activation lock on it, there's no icloud lock on it, so I don't understand why it won't activate. 

I've tried different sim cards from different carriers and they work in the phone, it shows the signal bars and 4G at the top, so I don't think it's caused by sim lock. 

I've tried activating the phone using both WiFi and carrier data but it's not working. Every time it takes me through the activation process it just says 'unable to activate'. 

Is there anything else I could do?

Update: It starts from the 'Hola' page, it says connect to WiFi, once connected I click next to go onto the next page, then it says 'it may take a few minutes to activate your iPhone' then after that an error message comes up saying 'Unable to activate' (like the picture inserted)