White belly mark could be a scar - I have a frog with a similar mark that resulted from an ornamental injury.
The black underneath the arms is called nuptial pads and means your frog is a male. The frogs do shed but the black arms has nothing to do with that fact.
The males do frequently make a mating call - I have a recording of the sound on my site Jenste Frogs under African clawed frogs, Breeding if you want to listen to it to compare.
Now,
What size tank is that? The tall types are really not the best design for a primarily bottom dwelling creature - - they benefit from floor space, not height.
What did she tell you to feed them? The best diet is Reptomin Sticks. Do not feed fish food of any sort, they are not fish and this food is nutritionally incomplete for their needs. Do not also only feed frozen bloodworms or beef heart. Bloodworms make a great treat but in my opinion beef heart should be avoided at all costs due to it's high fat content.