RIP tricycle

Three and a bit weeks ago my tricycle died.
It started by dropping the chain, so I ended up walking more than cycling. Then on the 13th of February, I set off to go somewhere. I thought that the chain had dropped off, again!.....but no, the gear assembly had come adrift, and after around 25 miles, my tricycle is no longer operable.
I am more than a bit unhappy about this. I ended up walking further than I can, and consequently have ended up back on my crutches, as I did something to my foot that means it hurts to walk with just a pair of sticks.
The vendor has briefly replied to my email, asking me to wait. But that's three weeks ago. I don't want it repaired, or replaced. I just want a refund of my money, as the tricycle is not fit for purpose. C
If they don't reply soon, I am going to leave extremely negative feedback on eBay, plus I bought with my visa card, so I might involve them. I really hope that I don't have to resort to that though.
As well as being angry, and hurt, I am sad that the tiny bit of freedom I thought that I had has been taken away from me.