Change Plan 3g - It doesn't work

Good morning.

I called 611 and it was offered me a new plan. 45US$ monthly with 2G of data internet, unlimited nationwide talk and text.

I switched my plan and since yesterday I've been trying to access the 3G unsuccessfully.

I googled it what problem could be happening and after 2h of research, I was told that because I use a Samsung S3 mini, a smartphone, the internet won't work. This 45US$ monthly plan is for basic phones only.

Well, nobody told me that before I switch my plan.

Now I can't access internet, and I can't change my plan again because to change it, I have to charge my account again, which I just did.

I'd like to know if AT&T could switch my plan to the 40US$ monthly, since I can't use the 45$ using my S3 mini.

Or, if AT&T could refund my money back so I can switch plan again.

Thanks.