Encrypt String AES Windows Phone 8.1

I'm making an app which will need to encrypt a string. I'm completely new to AES encryption.

I have to code that runs on the server to encrypt.

public static string Encrypt(string text, byte[] key, byte[] iv, int keysize = 128, int blocksize = 128, CipherMode cipher = CipherMode.CBC, PaddingMode padding = PaddingMode.PKCS7)
{
    AesCryptoServiceProvider aes = new AesCryptoServiceProvider();
    aes.BlockSize = blocksize;
    aes.KeySize = keysize;
    aes.Mode = cipher;
    aes.Padding = padding;

    byte[] src = Encoding.UTF8.GetBytes(text);
    using (ICryptoTransform encrypt = aes.CreateEncryptor(key, iv))
    {
        byte[] dest = encrypt.TransformFinalBlock(src, 0, src.Length);
        encrypt.Dispose();
        return Convert.ToBase64String(dest);
    }
}

I already have this, with a library Bouncy Castle, but I can't seem to find a simple example.

byte[] key = Encoding.UTF8.GetBytes("[SECRETKEY]");
            byte[] iv = Encoding.UTF8.GetBytes("[IV]");
            var cipher = CipherUtilities.GetCipher("AES/CBC/PKCS7Padding");

            cipher.Init(true, new KeyParameter(key));

If it can help I also have the code which runs an Android client. Let me know then I can post it.

You can use the PCLCrypto library, there's a nuget package available (Install-Package PclCrypto)

From https://github.com/AArnott/PCLCrypto/wiki/Crypto-Recipes:

Perform AES encryption/decryption

byte[] keyMaterial;
byte[] data;
var provider = WinRTCrypto.SymmetricKeyAlgorithmProvider.OpenAlgorithm(SymmetricAlgorithm.AesCbcPkcs7);
var key = provider.CreateSymmetricKey(keyMaterial);
byte[] iv = null; // this is optional, but must be the same for both encrypting and decrypting
byte[] cipherText = WinRTCrypto.CryptographicEngine.Encrypt(key, data, iv);
byte[] plainText = WinRTCrypto.CryptographicEngine.Decrypt(key, cipherText, iv);

The cipherText variable is the encrypted data, plainText is the encrypted variable decrypted again