Add APN (+ Button) Option Missing

So my gf and I both have the Xiaomi Mi A2, her works perfectly, but when I tried to setup mine, I realized I had no data connection. In order to make it work with my provider, I must configure a new custom APN but for some reason, the button to add a new one is missing. I´ve checked, however, my gf's mobile, despite being apparently the same in every aspect, she has such button. Then I thought there must be some differences between both devices operating system's version, so I wonder if is there a way to compare both to check what I'm missing in order to have the option that I need? If not, any way to fix this would be really appreciated. Thank you in advance