title: TypeError: this.contactService.verifyContact(...).subscribe is not a function
body: <p>I've seen other questions about it, but none could help me.</p>
  <pre><code>    createEmergencyContactBoat(emergencyContactBoat: EmergencyContactBoat, number: string) {
          return this.db.connect().then(connection =&gt; {
              return this.contactService.verifyContact(number, connection).subscribe((result: any) =&gt; {
                  if (!result){
                      throw new Error(ErrorMessage.CONTACT_DONT_EXIST);
                  } 
                  emergencyContactBoat.emergencyContact = result.id
                  return connection.collection(this.collection).insertOne(emergencyContactBoat);
              })    
          })
      }
  </code></pre>
  <p>The class contact-service:</p>
  <pre><code>verifyContact(number: string, connection: any ) {
          return connection.collection(this.collection).findOne({emergencyContact: {$eq: true}, 
              contact: {$eq: number}}).then((result: any) =&gt; {
                  return result
              })
      }
  </code></pre>