Wing mirror arm loose ??

My wing mirror arm moves up and down with wind/vibration and eventually gets pushed in/folded back towards the vehicle. It is a new arm purchased at the Peterborough L/R show this year. Am a little pigged off to say the least.
It is secure at the hinge and the mirror is tight to the ball, it's the ( against Spring tension or internal workings of the mirror.
Anyone know of a fix for this or is it a case of a new mirror .

Thank you in advance.

Aftermarket ones are generally poor. They don't have the same mechanism as original LR ones. I had to put extended arms on for caravan towing and got them from Paddocks. They're just about OK but do tend to move up and down with wind gusts and HGV air movement on the motorway. I think they would probably fall off over 65 mph.

I had this with mine and greatly improved things by removing the mirror head (cap bolt or bolts can't remember twas a few yrs ago) , I drilled and retapped the plate next size up (can't remember size's) and after cleaning the bits up, used quality stainless steel cap bolts to refit. I found the larger bolts could be tightened much more and the wobble was much less. I used a ratchet and extension with the correct bit to really get it tight but had to revisit them a couple of times to give them another tighten over a few weeks. They haven't moved now for around 2 yrs.
The standard cap head bolts on mine were very poor quality with shallow drive heads which made getting a good purchase awkward and the rusty male/female threads didn't help.
The plate with the female thread is quite manly and easily took the increased thread size and torque.