I intend to switch back to Digi Prepaid since my usage is not that much under 1 Family Postpaid. Which route would u recommend?

1) Digi Postpaid --> Celcom Blue Prepaid --> Digi Prepaid
2) Digi Postpaid --> Hotlink Prepaid --> Digi Prepaid

Which 1 will cost the least to MNP?
Do I get 1 year free validity once i got back to DIgi Prepaid??

Everyone, Last time I already said I intend to switch my Supplementary 1 Family Plan number to Digi Prepaid,
But I found out that

1) It is impossible to port out from supplementary line to become a prepaid line no matter which service provider. Celcom CS said that all number along with the main number should be ported out together!!!!!!
-- Since I wan my number alone to switch only, is there any other way to do so? (Celcom, Hotlink, Digi all do not allow supplementary line to port out... )
(This also means that the initial plan : Digi postpaid > Celcom prepaid / Hotlink > Digi Prepaid cannot be done)