There should still be suitable cutting material on your Pieris 'Forest Flame' to take cuttings now. What type of shoots have you been using? Are they the youngest ones?
Any time between late spring and autumn is fine for trying to strike these cuttings. Take 8-10cm long cuttings, I think the key is the type of wood you select. You need to be looking for shoots that are from this year but they have aged a liitle and our slightly firmer than the youngest shoots but not too woody.
Cut out the growing tip from each cutting you take and keep 5 or 6 leaves. The cuttings need to be nodal i.e. directly below a leave joint on the stem. Use hormone rooting powder/solution. Also very important, basal heat is required, 60F is ideal. If you don't have the necessary kit, stand the cuttings on top of the boiler or in the airing cupboard. I would seal whatever container the cuttings are in a clear polythene bag to reduce water loss from the cuttings.
I would not give up if the leaves fall off, you are looking for signs of new growth in the buds on the stem where the leaves join the stem.
It may take 2 months for the cuttings to root. Let me know how you get on.