So I had a new cambelt water pump and tensioner fitted to my 04 wrx 1200 miles ago! All of my marks line up on the cam pulleys but my tensioner piston keeps collapsing and causing the tensioner wheel to rub on the crank sprocket. Can the cambelt be on too tight at the top and forcing it up or just a faulty tensioner?? 

None of parts in that pic look particularly new .
tensioner and toothed idler don't look new and back of the belt have a lot of marks for 1200 miles !
Is the crank gear belt guide removed for investigation/photo or missing !?
If none of that oem mainland japan made I would throw it in bin and buy the oem kit from ICP.
About only kit we use these days as even bigger name aftermarket kits have some dubious quality chinese parts in them these days .
Hard to tell what exactly wrong from just that 1 picture but the whole job needs evaluating and top quality parts used . It very easy job and the oem complete kits from ICP are not expensive so doing job to good standard is achievable for sensible cost/effort .
I would assume it mainly tensioner issue and hydraulic seals failed but it not an area we skimp on or want run on assumptions alone so whole lot needs checking and ideally I would likely want replace whole timing belt parts including the belt and all idlers .