The three variations after "recommended" all have the same meaning.
The three variations with "said" have different meanings:
"I said that you kept silent." suggests that you stayed silent while (or during) some event.
"I said that you keep silent." suggests that you are normally a silent person. Perhaps you seldom speak. Perhaps you move quietly when you walk.
"I said that you should keep silent." suggests that you were instructed to be silent but that you disobeyed, that you spoke or made other noises. It could also be used in the sense that you were instructed and you obeyed that instruction, however I would expect some additional words in this case. Perhaps to a child you would say "I said that you should keep silent and you did, so well done."
For the last variation where an instruction is given the word "keep" can be replaced with "be". When I think about this change I believe that "be" is more usual with an instruction. The terse order to "be quiet" was often said to me as a child.