There is no way you could truly lose your telephone number. Your telephone number(s) are based off of your Business ID Number, or NIIN. If Frank’s NIN is 52022554377, then all 10 of his numbers will begin with 52022554377. Therefore, he owns 520225543771 even if he never activated it. No one else can have 520225543771 because your NIN is 52022554377. The only way you could lose your telephone numbers is if your NIN was to change. The only reason I could see a person losing his NIN is if they went into witness protection. In which case, their old NIN is effectively terminated, and anyone having your old telephone numbers will no longer work.
This means that the telephone numbers are yours, and yours alone. You can never lose your telephone numbers for any reason with exception of above. You are responsible for paying for service on any of your active numbers.