eth_call returning "0x"

[hub-il]

We are trying to use the JSON-RPC "eth_call" method to return the total supply of a token. For example:

{
    "jsonrpc": "2.0",
    "method": "eth_call",
    "params": [
      {
        "to": "0xdAC17F958D2ee523a2206206994597C13D831ec7",
        "data": "0x18160ddd"
      },
      "0x894E426"
    ],
    "id": 1
  }

But instead of getting the supply, the result is always 0:

{
    "jsonrpc": "2.0",
    "id": 1,
    "result": "0x"
}

Is it possible to use the "eth_call" method to get the total supply? If so, what are we doing wrong, and if not, is there an alternative method?