Lead conversion with following APEX code.
Database.LeadConvert leadConvert;
leadConvert = new database.LeadConvert();
leadConvert.setLeadId(leadId);
leadConvert.setDoNotCreateOpportunity(true);
LeadStatus convertStatus = [SELECT Id, MasterLabel FROM LeadStatus WHERE IsConverted=true LIMIT 1];
leadConvert.setConvertedStatus(convertStatus.MasterLabel);
List<Database.LeadConvertResult> leadConversionResults = Database.convertLead( new list<database.LeadConvert>{leadConvert} );
Lead leadData = [select id, status from lead where id = :leadId limit 1];
leadData.status = 'Qualified';
update leadData;
Issue:
If the account and contact are already in SF then it is updating the already existing account and contact but the problem is it created new account and contacts as well. How can prevention of account and contact can be done?