Commenting to also see some recommendations 👀
A couple of years ago I was also on the look for a good course on this topic but unfortunately didn't find anything suitable. I found a lot of it was a bit too generic for our support team and wasn't fully relatable.
We ended up creating a 'soft-skills' training ourselves as it meant we could be more specific to what our support team was dealing with.
We began the training with the basics, such as explaining empathy, and how to be an active listener. We just used some short youtube clips60 to help explain and keep it engaging.
We then created some exercises where we found some old conversations with some difficult customers and did a workshop where we got our agents to create the 'perfect' responses to them. We can then compare these with how the original agent responded and discuss as a group how we could improve our handling of these situations.
I can definitely recommend having some type of group discussion with real examples, as this is super relevant for your agents, as you will be talking about real scenarios that have happened and could happen to your team. The discussions are a great way to learn from your own agents what works/does not work and can really help you forge your own 'voice' for responding as a unified team when you face these customers!
Make sure to document your findings from the training and create a 'guidebook' for your agents to have for when they face a difficult customer.