What a horrible unwelcoming bunch of people! I have to say I would try the other club, you might be pleasantly surprised. Even if they don't offer quite as much maybe you can make some suggestions for changes once you get to know some people.
I definitely would email (I think you are brilliant for not telling them to feck off on the day btw)
If you want to stay 'in' with them you could email something along the lines of:
'Having recently moved to the area I was looking forward to meeting other local horsey people at the riding club. While my horse is off the road I thought helping would be a good way of doing this. However, I have to ask if today was typical? I had hoped to MEET some people, as well as work of course. It would have made such a difference if anyone had been a little bit welcoming - or even spoken to me (other than the person who shouted 'Oi stick girl' when trying to catch my attention when I was measuring a fence!)
I suppose I have been used to a club where new members were made very welcome and 'helpers' are at least a little appreciated.
As I say, maybe I hit on a bad day at the club? I do hope so as I was looking forward to being involved but feel very deflated and disappointed by my experience today'
Just a suggestion anyway - it should make them feel bad!
I'm glad you complained because no, you are not over-reacting. We don't expect medals but you should have got a drink/food and someone checking you were okay, esp as you are new!
Hope it was a one-off for the club and if not, find another who will be grateful for your help.
I'd be tempted to spend my spare time helping an equine charity or something instead. How flaming rude of them. No wonder people get the wrong idea that equestrianism is elitist and snobbish with those kind of attitudes!
I don't think you over-reacted at all. Not sure how I would have replied to the 'Stick-girl' shout, possibly I would have replied with, 'Are you talking to me, fat ar5e?'