Now then

[Isbell]

Now then, it did exist, this was a real fact.
Can I refer the phrase of 'now then' to 'from the past to the present days'?

[Mister Micawber]

No. 'Now then' is a fixed phrase.

"A sentence opener indicating that a new topic is being opened or that the speaker is getting down to business. (Expressions such as this often use intonation to convey the connotation of the sentence that is to follow. The brief intonation pattern accompanying the expression may indicate sarcasm, disagreement, caution, consolation, sternness, etc.) "Now then, where's the pain?" asked the doctor. Mary: Now then, let's talk about you and your interests. Bob: Oh, good. My favorite subject. Sue: Now then, what are your plans for the future? Alice: I want to become a pilot. "Now then, what did you have in mind when you took this money?" asked the police investigator.
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Native English teacher at Mister Micawber's

[Isbell]

Now then, without the whole context, it is very hard to say for sure if that sentence is used to express sarcasm, caution or something else. Anyway, many thanks for the explanation.