Cut substring between character
When you execute:

select total
from (SELECT regexp_substr('Espacio Asignado:358898204672: Espacio Usado:355976458989: Espacio Reclamable:2921745683:','[^:]+', 1, level) total
      FROM DUAL
      connect by regexp_substr('Espacio Asignado:358898204672: Espacio Usado:355976458989: Espacio Reclamable:2921745683:','[^:]+', 1, level) is not null)
where   REGEXP_LIKE(total, '^[[:digit:]]+$')
/


You get all the numeric values in the string.