Unfortunately you are learning the hard way that some shops are either ignorant about the stock they carry or will lie to make a sale. Don't believe anything any of them says till you have more experience; research any fish on-line before buying and you will avoid any future problems. When you have had more experience, you will be able to tell which of your local shops can be trusted and which can't. Until then, assume none of them can be trusted.
Both types of frog have webbed back feet but only dwarf frogs have webbed front feet. If you head down to the invertebrate, amphibian etc section of the forum you'll find a pinned thread on frogs and advice there on the kind of tank a clawed frog will need in the future.
Specialist frog food is best for frogs. I use zoomed frog and tadpole food for my dwarf frog, I had to get it on-line as I couldn't find a shop that sells it. I think there is another make too in the UK, but I haven't seen that in a shop either. In the USA, the one to get is HBH frog food.
Since it seems you have a clawed frog rather than a dwarf frog, when it gets bigger it'll be able to eat reptomin sticks.