Poor thing, it looks as if frosted flowers and hungry leaves, although hard to know for sure.
Previous to the last couple of years, did you get better performance?
The non-flowering last year is almost certainly due to dry roots the August before, it's so hard to overcome the problem in pots, where a brief spell of dryness in summer kills the flowering potential for the following year.
Of course the non-flowering could have been a pruning issue if they had been pruned between July and March...
How far north are you? Did you get any frosts the past month?

Hi Pani, as Td said the flowers turning brown can be frost related. However it has been relatively mild this spring. I have have had issues with Camellias "not flowering" in pots, in fact I also have 2 that have never flowered. I have had them for 3 or 4 years. The one I have in the ground, is fabulous, healthy and flowers well. I also will watch replies to your question with interest.

PS Sorry I am unable to advise on the yellow spotted leaves.

Those black deposits on the back of the leaf, visible in the top half of the picture - are they aphids or just black dots?

Check all stems and backs of leaves to see what you can find - perhaps scale infestation or other evidence.

Thank you all for your responds. I live in midlands hence no frost last winter. I didn't do any pruning too. They didn't flower over the last few years at all( in fact they had flower only the first year we got them!) we only changes the compost last year.
I read somewhere that they do better in pots rather than ground because of their acidophilic nature.
Bamboo, congrats on your sharp vision! I looked more carefully on the stems and leaves to see any aphid, all I could see were ants and small spiders. Just one of the leaves had a white larva that I have no idea what it is! I'm going to update my question with new photos of the leaves. Will be grateful for your thought.
Many many thanks for your time.
Pani

Camellias grow perfectly well in the ground, in fact, they often do better there - but not if your soil is limey/alkaline.