According to some web site, "言う" means to say generally.

"云う" means to say with that somebody said , "謂う" means to say with common knowledge.

But people don't distinguish each , and write ”言う”usually. We can see "云う" or "謂う" in novels sometimes.

I don't remember when I wrote “云う” and “謂う” last time or It might be never used.