Difference between 'get down to' and 'get through'

[Pasban110]

English Language Tests, Intermediate level

ESL/EFL Test #828 "Common 'Get' Usage (2)", question 2

I don't know how to get ......... to you! If you come in late one more time, I will fire you. Do you understand?

(a) off
(b) on
(c) through
(d) down

English Language Tests, Intermediate level

ESL/EFL Test #828 "Common 'Get' Usage (2)", answer 2

I don't know how to get through to you! If you come in late one more time, I will fire you. Do you understand?

Correct answer: (c) through

Your answer was: incorrect
I don't know how to get down to you! If you come in late one more time, I will fire you. Do you understand?
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Hi,
What's the difference between 'get down to' and 'get through'.

Many thanks.

[Mister Micawber]

Get down to = implement
Get through to = communicate with
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Native English teacher at Mister Micawber's