Welcome to the Community Forum and thanks for your post. I'm sorry to hear that you are experiencing a problem with your mobile losing your voicemail number. I just need to double check that you've set your voicemail up, first, by calling 222 from your handset. Next, please verify that the voicemail contact is being entered correctly on the LG K8, are you following these steps:
2.Touch the Add contact icon.
3.Touch Phone contact.
4.Touch the required location you wish to save the new contact.
5.Enter the contact name Voicemail.
7.Enter the voicemail number +447953222222
9.The voicemail number has been saved.
Please let me know if you've done this already and the contact is still disappearing from your phone.