Property manager refusing to send ex-tenant to collection because I've found a new PM

[Sam Quirke]

Hi all, I have a rental in MO that was trashed by its last tenants in August, and has cost ~$20k to make ready.

My PM at the time was adamant about sending the tenants to collections once we had a clear idea of the figure they're responsible for, which is about $10k. In the 2 months since, they've warned the ex-tenants multiple times over email that they'll be sent to collection if they don't pay, and they haven't.

In the meantime, I've come to realise the PM is incredibly incompetent and unreliable, and have found a new one.

But now that I've given notice that I'm switching this month, the old PM is outright refusing to send the ex-tenants to collections as they are "no longer under contract, our partnership is considered terminated and we are not able to represent you in any way."

The new PM says this isn't something they can help with and won't be getting involved, so I feel completely let down and abandoned by the old PM, and at a loss as to what to do.

1. - Is this a reasonable stance for the original PM to take?
2. - Can I force them to send the tenants to collection?
3. - Can I send them to collections myself as a last resort?

For context, I'm an out-of-country investor who tries to be as hands-off as possible.