code: @Override
      public boolean cancelNumber(PhoneNumber phoneNumberObj) {
          String phoneNumber = phoneNumberObj.getPhoneNumber();
          String numberToRemoveFromVi = phoneNumber;
          if(numberToRemoveFromVi.startsWith("+1")){
              numberToRemoveFromVi = numberToRemoveFromVi.replaceFirst("\\+1", "");
          }
          phoneNumber = numberToRemoveFromVi;
  
          if (!isValidDid(phoneNumber))
              return false;
  
          if (phoneNumber != null && !phoneNumber.isEmpty()) {
              final StringBuilder buffer = new StringBuilder();
              buffer.append("<request id=\""+generateId()+"\">");
              buffer.append(header);
              buffer.append("<body>");
              buffer.append("<requesttype>").append("releaseDID").append("</requesttype>");
              buffer.append("<item>");
              buffer.append("<did>").append(phoneNumber).append("</did>");
              buffer.append("</item>");
              buffer.append("</body>");
              buffer.append("</request>");
              final String body = buffer.toString();
              final HttpPost post = new HttpPost(uri);
              try {
                  List<NameValuePair> parameters = new ArrayList<NameValuePair>();
                  parameters.add(new BasicNameValuePair("apidata", body));
                  post.setEntity(new UrlEncodedFormEntity(parameters));
                  final DefaultHttpClient client = new DefaultHttpClient();
                  if(telestaxProxyEnabled) {
                      addTelestaxProxyHeaders(post, ProvisionProvider.REQUEST_TYPE.RELEASEDID.name());
                  }
                  final HttpResponse response = client.execute(post);
                  if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
                      final String content = StringUtils.toString(response.getEntity().getContent());
                      if (content.contains("<statuscode>100</statuscode>")) {
                          return true;
                      }
                  }
              } catch (final Exception ignored) {
              }
          }
          return false;
      }
docs: /*
  (non-Javadoc)
  @see PhoneNumberProvisioningManager#cancelNumber(java.lang.String)