TNT Express added additional charges without consent - shipping Banggood order

TNT express shipped some goods for my via Banggood. The goods were worth ~R3000, the originally quoted shipping fee was ~R700, excluding any possible customs charges that may be incurred. Once the goods arrived, TNT then decided to charge me an extra ~R500 fee for 'customs clearance' in additional to the customs fees. So TNT in effect almost double their shipping fee. Now they won't release the goods unless I pay. Its such brazen bare faced ******ion. You can't just increase your shipping fees as you wish and then hold my goods hostage. Most frustrating is I'll end up paying it because I'm cornered here - which I guess is their business model.