I have a dwarf apple tree and I pruned it just over a month ago and it has already all grown back

The new growth on the apple tree will need to be removed.  Apple trees should be pruned when they are dormant for best results.

With deciduous trees, we recommend pruning once all the leaves have fallen off. That way you can see the skeleton of the tree and find the ideal shape.

Ideally prune stems so they are facing outwards from the main trunk. Prune any crossing or rubbing branches.  

When pruning, remove anything that is dead/diseased/damaged. The general rule is to remove no more than a third of the total foliage to reduce plant stress.  

Apply Lime Sulfur during dormancy to budswell to help control fungal diseases on apple trees.

Try 'Yates Lime Sulfur - Insect and Disease Control' to control a range of insect pests and fungal diseases on roses & ornamentals, citrus, grapevines, apples, some stone fruits, tomatoes & vegetables. Click here for more info on this product: https://www.yates.com.au/product/garden-pest-control/yates-lime-sulfur