Max with Left Join

Hi,

I need to extract from a database of an association, the name of the associate and its last paid share, but after a day trying I simply cannot extract that data.
The table senhas represents the shares, the table associados the associate data and senhas_associados, represents the shares paid by an associate, as it was a many to many relationship.
To query this, I'm trying to query the share with the maximum id (senha) which is in seassoc_senha_id in senhas_associados which represents a paid share.

Here's what I've tried so far:
Firstly, I've tried this statement, the output is the required, but it doesn't show associates who haven't paid any share which is needed (no records in senhas_associados):

SELECT assoc_nome, senha_desig
FROM associados, senhas, senhas_associados
WHERE assoc_id = seassoc_assoc_id
AND seassoc_senha_id = senha_id
AND seassoc_senha_id IN (SELECT max(seassoc_senha_id)
FROM senhas, senhas_associados
WHERE seassoc_senha_id = senha_id
AND seassoc_assoc_id = assoc_id)

the output:
assoc_nome senha_desig
Carlos Costa Maio
Rodrigo Abril

I've even tried adding this:
SELECT assoc_nome, senha_desig
FROM associados, senhas, senhas_associados
WHERE assoc_id = seassoc_assoc_id
AND seassoc_senha_id = senha_id
AND seassoc_senha_id IN (SELECT max(seassoc_senha_id)
FROM senhas, senhas_associados
WHERE seassoc_senha_id = senha_id
AND seassoc_assoc_id = assoc_id) OR senha_desig is null

To no avail, the output was the same.

Then, I've changed the "tactic" and went to left join:
SELECT assoc_nome, senha_desig
FROM associados
LEFT JOIN senhas_associados ON associados.assoc_id = senhas_associados.seassoc_assoc_id
LEFT JOIN senhas ON senhas.senha_id = senhas_associados.seassoc_senha_id

The output:
assoc_nome senha_desig
Carlos Costa Abril
Carlos Costa Janeiro
Carlos Costa Fevereiro
Carlos Costa Maio
Rodrigo Janeiro
Rodrigo Fevereiro
Rodrigo Abril
Pedro Soares NULL

Now it shows NULL's, but I can't find where to put the max function.

So I'm requesting your help, since today's afternoon that I'm stuck with this.

Thanks everyone,

Regards.

I've attached the relational model of the involved tables.

Attached Images

relational_model.PNG (12.1 KB)