In my opinion, you have everything to ask the dealer where the car was repaired, to solve the problem without further cost.
I can not advise you to replace the charger but, as it is an expensive replacement, I can advise you to ask them to do the same as the Renault dealer did here, in Portugal. He asked Renault for a new charger, who came to the consignment, that is, in case the problem was confirmed to be the chearger, I would stay with him, and pay the price. If it were not a problem for the new chearger to solve, Renault accept the devolution.
So, we can order the charger, certain that we would not spend money on the new element without result.
If you already have some money spent on a particular dealer, you should not go to another, without exhausting the solutions that the dealer where the car was, can present you. In my opinion he is obliged to solve the problem. I Think you don’t present them the posible solution or prupose them the way to solve it. You present the car with a problem, and certainly it was they who made the diagnosis and presented the possible solution. And they charged you a certain amount to solve it. If it was not resolved, either they refund the amount spent or solve the problem …
If you go to a new dealer, will start a new process and present you a new budget for resolution, as he has no responsibility for the work done by the other …
About the distance, a similar situation happened to me. I went to the dealer in my area of residence (+/- 25 km) and did not like the way they worked, doubting even the skills to work in this type of vehicle. I pick up the car, put it in a trailer and went to a dealership 85 km away, and I can guarantee one thing: Since that day, any problem I will have in my twizy, it will be in that more distant dealer that I will solve it .
Wish you Good Luck.