How to order results of related models in laravel?

I have three model ProductCategory ,Product and ProductPrice . My models are like this

ProductCategory.php

  public function product()
    {
        return $this->belongsTo('App\Models\Product');
    }
  public function category()
    {
        return $this->belongsTo('App\Models\Category');
    }

And my Product model is like this

 public function category()
    {
        return $this->hasOne('App\Models\ProductCategory');
    }

    public function price(){
       return $this->hasMany('App\Models\ProductPrice');
    }

Now i want get all the product of a category and sort them by name/price as requested. My query for this is

        $query = ProductCategory::with(['product'=>function($q){
          $q->whereHas('price',function ($q){
              $q->where('quantity','>',0);
              $q->where('status',1);
          });

        }])->whereHas('category',function ($q) use ($cat){
            $q->where('category_slug',$cat);
        });

switch ($request->get('sort')){
                case 'price':
             $query->product()->price()->orderBy('amount','asc');
                    break;
                case 'name':
                        $query->product()->orderBy('title','asc');
                    break;

            }
  $data['result']=$query->paginate(30)->toArray();

So i was expecting that this query will return me product from the category and will sort them by price or name as requested. But instead of that its giving me error saying

Call to undefined method Illuminate\Database\Query\Builder::product()

I have followed these threads but no help

Laravel orderBy on a relationship

Laravel Eloquent: How to order results of related models?

https://laracasts.com/discuss/channels/eloquent/order-by-on-relationship

And few more these are the one i found to be close to my problem. Can anyone please help me with the query Thanks

via Chebli Mohamed