How to submit apex form to a specific action url?

Question

I am working on a web2lead form which updates a record after it's submitted. I converted the web2lead to a visualforce page and I am trying to use a standard controller extension to update the record when it's submitted. But I am getting a Invalid Page Redirection error and I think it's because the apex form is not submitting to the right url. Below is my code:

VF:

<apex:page standardController="SVMXC__Service_Order__c" extensions="BEC_Web2LeadExtension" docType="html-5.0">
   <apex:form html-action="https://test.salesforce.com/servlet/servlet.WebToLead?encoding=UTF-8" html-method="POST">
    <apex:commandButton value="submit" action="{!submitAndUpdate}"/>
   </apex:form>
</apex:page>

Extension method:

    public void submitAndUpdate(){
    //controller.save();
    SVMXC__Service_Order__c woRecUpdate = [select id, Submit_lead__c from SVMXC__Service_Order__c where Submit_lead__c = true and id=: woRec.id];
    if(woRecUpdate != null){
        woRecUpdate.Submit_lead__c = false;
        update woRecUpdate;
    }

So my question is how do I submit the form to the url and also update the record the form is submitted from?

Thanks in advance for any help!