You can use the getCode API. If that call returns 0x, there is no contract at that address. If it returns anything other than 0x, there is a contract at that address.
As an example:
The pool you are mining for probably only pays you once you reach a certain minimum, like 0.1 Ethereum. So you may need to mine a bit more until you are actually paid.
You should be able to keep track of how much you have mined in that pool.
On ethermine.org you are able to search for the "Miner Address", you put the public address of your wallet ...