Both sentences have minor issues even though they may be considered good in Japanese as a foreign language. At least, both are grammatical.
「から」 actually sounds more casual/informal than many J-learners seem to think. That is the impression that I get from speaking to them. The more formal words with the same meaning would be 「ので」 and 「ため/ために」.
With 「です/でした」, which is not particularly polite or formal as some learners seem to think but, nonetheless, is on the politer side, you would want to avoid using 「から」.
In both of your sentences, 「から」 and 「でした」 are used in combination, which is what I called an issue at the beginning.
One more thing. You would sound nicer and more apologetic if you used 「行けませんでした」 than if you used 「行きませんでした」. Former means "I was unable to ~~" while the latter means "I did not ~~".
Thus, the sentence that I would recommend is:
Your second sentence sounds too polite in an awkward way, using 「ありませんでした」 in the sub-clause when the main clause contains a 「行きませんでした」. That is a little too much for a short sentence like that.