If you’ve been charged for collecting an Amazon parcel, then there’s a good chance you ordered it from an Amazon Marketplace seller.
An Amazon Marketplace seller is a third-party vendor using Amazon’s website to sell their own products and is not part of the free collections offer. They’re an independent retailer and handle their own deliveries.
You can find more information here.
When you’re shopping on Amazon, check the items product page - it should tell you if it’s eligible for click & collect.