Yes Marvel has a Captain Marvel (not MAr-Vell, BOO!) and DC can't use the name due to Marvel having the trademarks.
Yet DC thinks Shazam is too close to Superman in terms of infringement.....
....which I can see to a point however there are differences between them too.
However money talks and Disney/Marvel have got money and successful movies unlike DC.
So perhaps the whole Captain Marvel trademark/ownership junk could now be resolved if DC receives enough cash? Bring SHAZAM as Captain Marvel into the MCU and comics.
Personally, I've always been of the opinion that DC shouldn't even try to call the guy Captain Marvel in stories. But I really cannot stand the character at all. The only Captain Marvel should be Marvel's.