For OkHttp 3.x, FormEncodingBuilder was removed, use FormBody.Builder instead
RequestBody formBody = new FormBody.Builder()
.add("email", "[email protected]")
.add("tel", "90301171XX")
.build();
OkHttpClient client = new OkHttpClient();
Request request = new Request.Builder()
.url(url)
.post(formBody)
.build();
Response response = client.newCall(request).execute();
return response.body().string();