When training anything introduce the behaviour, in this case recall.
When that is ok then you can increase distance duration and distraction.
You have increased distraction too quickly.
You have also not completely taught the recall if he is not coming right up to you.
Start with that at home. I dont do collar grab and recall at the same time for some dogs this can put them off coming to you. (I do collar grabs when the dog is just chilled next to me)
Blow your whislte and reward at your feet.
Blow the whistle and reward between your legs
Blow the whistle and rewards throwing the treat through your legs
Get your dog excited to wonder where the treat will be
Sometime put the lead on other times run away after giving the treat and let them chase you
Vary the end of the recall.
The reason the recall is not so successful out and about is that there are too many distractions. Just sniffing the grass is amazing if you are a wcs 
So going from home garden to the walk is too much of a distraction.
Think of it from a working cockers point of view. He knows the garden inside and out, smelled all the smells, seen all there is to see.
Then you go to his walk. The smells, the movement, the air, the atmosphere, the leaves, the squirels, it is SOOO exciting. The environment in this situation is competeing against your whistle and reward.
So what to do?
Carry on in the home and garden, then choose a boring place. This depends on your dog but a quiet small area is a start. Have your dog on a long line and practice here. Dont let the dog go too far away from you and reward as if they are the best thing ever. This is hard for them and they need encouragement to master the recall in a different area.
So build up what you are doing considering the distractions from a wcs point of view.
Remember there is no hurry to get this right, if you have to use a long line for a bit that is fine. Everyday is a school day and the slower you go with this the better it will be in the end.
The problem with upping the reward eg find a new reward eg ball or tuggy toy is that you will rarely win consistently against the environment. What you are aiming at is a reflex reaction to the recall command which takes time and practice
It is very common to feel like you are going backwards at the teenage stage. You are not and all your foundation work will pay off. Stick with it be consistent and you will have a fab recall. Dont doubt yourself