How can I change checkbox value from database?

I am facing a problem in checkbox they are always checked. When I add an object in database contains checkbox, it always shows checked checkbox when I open the edit page in my application !

this is my ts file :

code: string;
  isDefault: boolean;
  obj: Typestation= new Typestation();
  constructor( private formBuilder: FormBuilder,private typestationservice:TypestationService) {
  }

  ngOnInit() {
    this.typestationservice.getTypeStationById(this.id).then(resp => {
      this.obj = resp;
      console.log("testtt",resp)
    });
    this.messageForm = this.formBuilder.group({
      code: [''],
      libelle: [''],
      isDefault: [''],
      active: ['']
    });
  } 
  onSubmit() {
    this.submitted = true;
    if (this.messageForm.invalid == false) {
      this.success = true;
      let obj = this.messageForm.value;
      obj.id = this.id;
      this.typestationservice.updateTypeStation(obj).then(resp => {
          this.exit();
      })
    }
  }

and this is my Html file:

   <div class="col col-xl-3 col-lg-4 col-md-6 col-sm-6 col-12">
        <div class="form-group row">
          <label for="isDefault" class="costum_Font-size">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</label>
          <div class="col-12">
            <mat-checkbox id="isDefault" formControlName="isDefault" class="form-control"  name="isDefault" ngModel  [(ngModel)]="obj.isDefault">
              isDefault
            </mat-checkbox>
          </div>
        </div>
      </div>

      <div class="col col-xl-3 col-lg-4 col-md-6 col-sm-6 col-12">
        <div class="form-group row">
          <label for="active" class="costum_Font-size">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</label>
          <div class="col-12">
            <mat-checkbox id="active" formControlName="active" class="form-control" name="active"  ngModel [(ngModel)]="obj.active">
              Actif
            </mat-checkbox>
          </div>
        </div>
      </div>

my model:

export class Typestation{
  public id: string;
  public code: string;
  public libelle: string='';
  public active: boolean;
  public isDefault:boolean;


}

Can anyone help me to fix this problem !