Hello, as I understand it God spoke to Moses on different occasions and gave him of course many other commands separate from what are called the "10 commandments".
Before and after the so called "10 commandments" are given in Ex 20, the translated phrase
"And the LORD spake unto Moses, saying"
is repeated over 100 times that I found in a quick search, then going into other things that the Lord said other than the 10 commandments.
http://www.blueletterbible.org/search/translationResults.cfm?Criteria=And+the+LORD+spake+unto+Moses+saying&t=KJV
I am not sure what in chapter 24 some atheist thinks proves contradiction. They are people who don't know the Bible and are purposely looking for things in English translations that they think don't make sense in a literalistic 100% repetitive way, somehow thinking if anything is ever stated in the Bible, when it is ever repeated it must be repeated in 100% the exact same way with the exact same word count or somehow there is a discrepancy/contradiction.
1 Tim 1:7 Desiring to be teachers of the law; understanding neither what they say, nor whereof they affirm.
I am sure there are various examples all through the Bible written as either 100% literal, simile, overview, saying, parable, metaphor, exact record or overview only record, or paraphrased.
When we don't understand anything we usually can find the answer in reading all the other verses related, and looking at the original languages since Hebrew and Greek are very different than English and sometimes things that grammatically read strangely in English make much more sense when you look at the original language.
We are clearly told that we do not have 100% of every single word Jesus ever said recorded either, so I don't expect we know every single word God ever said to Moses either, but we don't need to. What is told and commanded is the revelation that we take into us and believe, not what word count was used to communicate those things which can vary and be of no significance if taken in proper context comparing scripture with other scriptures at all times.
John 21:25 And there are also many other things which Jesus did, the which, if they should be written every one, I suppose that even the world itself could not contain the books that should be written.