Inserting value into lookup field using esq inside web service

Hi all,

I am trying to insert a record to an entity using esq as follows in my web service.

[OperationContract]
        [WebInvoke(Method = "POST", RequestFormat = WebMessageFormat.Json, BodyStyle = WebMessageBodyStyle.Bare,
        ResponseFormat = WebMessageFormat.Json)]
        public string InsertCaseESQPostForSATS(DebitCardDataForSATS debitCardData)
        {
            try
            {
                var caseSchema = SystemUserConnection.EntitySchemaManager.GetInstanceByName("SBLSRM");
                var entity = caseSchema.CreateEntity(SystemUserConnection);
                entity.SetColumnValue("SBLAccountNumber", debitCardData.AccountNo);
                entity.SetColumnValue("SBLService", debitCardData.ServiceId);
                
                entity.SetDefColumnValues();
                var result = entity.Save();
                return result.ToString();
            }
            catch(Exception ex)
            {
                return ex.Message;
            }
        }

Column 'SBLService' is a lookup column and I am having problem while inserting a record, says, "Value 'SBLService' was not found.". I have checked and confirmed that the object has the column and is published fine. Can somebody assist me on this? How can I set value for a lookup column?