Are there any difference between” etc.” and “and so on”? What cases I shouldn't use “etc.” or “and so on”?
The abbreviation "etc." stands for "et cetera" which is Latin for "and the rest". But its common meaning in English also include "and so on".
So these two terms, "et cetera" and "and so on" are basically equivalent. Using one vs. the other is a matter of style more than anything else.
If I had to distinguish between them the usage of "etc." or "et cetera" is more common is written English especially where the purpose of the writing is more formal. The usage of "and so on" seems more common in oral communication but I am not aware of any hard-and-fast rule on this.