I know more about fish than I know that about frogs. I will say this gulper catfish are one of my favorite fish(its on the top 3). But they are expensive as a heck hole. They can run up from 200bucks to 400bucks or more. Ived seen them at some auctions. Ived seen them online(Very very very rarely). Ived seen them in some stores(only once). Their price is extremely high. I hear you on that one. You have to have some experience under your belt to even keep one. Not because its hard to care for. But because you dont want to screw up and having it die and then flushing down a 200-400dollar fish. Sometimes they even run up to 600bucks!!! Ill say this. If you have enough money for that Iam sure youd have enough to get a batch(joke-money wise). Animals arent perfect. Just because you give the animal proper care, and everything they need. Does not mean itll be a 100% safe. Some even die randomly. We are not gods. We cannot go like "HUSHA! I COMMAND YOU TO LIVE AND NOT DIE!". It doesnt work like that. In nature alot of the animals that are born die within their first or second year. Making it to adulthood is actually a rare site in nature. But since animals breed by the millions then they have some chance of survival. On an enclosure they have 80% of survival; the other 10% is actually on the animal itself and luck and thats if its captive bred. If its wild caught chances are lowered to atleast 65%! Maybe even less. Point is=dont beat yourself up for it. Everyone makes mistakes. You said you are a starter on frogs right? Well there ya go. You kept a wild animal and it lasted a long time with you. Thats pretty good. Alot of people who literary JUST start out and go out and buy something extremely exotic end up having the animal die within a week or two. Also the "Ease" of care is not something to be taken lightly. Its not a test. When we say something is "Easy" to take care of it doesnt mean it wont die. It just means its easier to care for than say a rare, endangered frog.
Like example:
Green Tree frogs(american)
Gray Tree frog
Dumpy's tree frog
Fire belly toads
Red eared sliders
Painted turtles
Yellow belly sliders
Ball pythons
Corn snakes
Are all easier to take care of than say
Dart frogs
mantellas
arrow frogs
tree toads
cormuttas
Soft shelled turtles
Bog turtles
Map turtles
Snapping turtles
Carpet pythons
Taiwan Red Rat snake.
You know? But you did a good job to return it and exchange it for a different and simpler one.