African Bullfrog (Pyxicephalus adspersus) from the low veld, its not the Giant Bullfrog (Pyxicephalus adspersus) from the highveld. I am saying this because it is already of a size that it has already started showing adult features and the line down its back for me is more African Bullfrog (Pyxicephalus adspersus), I have found Giant Bullfrog (Pyxicephalus adspersus) in the highveld of the same size as yours and they already have all the adult features.

Here is something to help you out: