Why 'double 9' and 'double 8' not recommended?

• In India we used to say '99' as double nine.
• But in foreign they don't know the meaning of double word.
• They spell as nine nine, eight eight like this.
• Because of this the communication problem arises. They can't understand our words properly.
• Because of this the 'double 9' and 'double 8' are not recommended.
• So we have to habituated to spell as nine nine, eight eight like this.