If you are not comfortable flashing firmware, consider these "top" alternatives:
Insert any SIM—Vodafone, EE, T-Mobile, Orange, or a cheap MVNO. The router will accept it instantly. huawei b311221 unlock firmware top
Say goodbye to the Vodafone or O2 logo. You get the clean, stock Huawei HiLink interface. If you are not comfortable flashing firmware, consider