The request was aborted: Could not create SSL/TLS secure channel using Restsharp

I am trying to connect the service file(.svc). from my c# code but i am getting message as

The request was aborted: Could not create SSL/TLS secure channel

The server accept only below Cipher code

The ciphers accepted are as per below:

TLSv1.2 128 bits ECDHE-RSA-AES128-GCM-SHA256 Curve P-256 DHE 256

TLSv1.2 256 bits ECDHE-RSA-AES256-GCM-SHA384 Curve P-256 DHE 256

Code:

string str = "<soapenv:Envelope xmlns:soapenv=\"http://schemas.xmlsoap.org/soap/envelope/\" xmlns:tem=\"http://tempuri.org/\">";
str = str + "<soapenv:Header/>";
str = str + "<soapenv:Body>";
str = str + "<tem:Logon>";
str = str + "<tem:logonRequest>";
str = str + "<tem:Username>XXXXXXX</tem:Username>";
str = str + "<tem:Password>XXXXXXX</tem:Password>";
str = str + "</tem:logonRequest>";
str = str + "</tem:Logon>";
str = str + "</soapenv:Body>";
str = str + "</soapenv:Envelope>";

Code:

ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;

ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback(delegate { return true; });

var client = new RestClient(url);
var request = new RestRequest(Method.POST);
request.AddHeader("Content-Type", "application/xml");
request.AddParameter("undefined", str, ParameterType.RequestBody);
IRestResponse response = client.Execute(request);

Tried the solutions as below

1) Added below line for TLS1.2 enable

ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;

ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback(delegate { return true; });

Thanks and Regards