SQL with SELECT and SUBSELECT to mount a chat

Question

Hello guys from Stackoverflow, I’m mounting the SQL below to mount a chat service user, which brings the list of all active conversations, but I’m having a problem, my SQL is bringing the latest message according to the Customer id, or if my message is last, it does not display, and I need to put a COUNT if there are new messages if the data_message is > that the data_message(current) for me bring notifications of how many messages are.

OBS: Table that stores messages: http://prntscr.com/jmkde8

SELECT CLI.id, CLI.nome, CLI.senha, CLI.email, CLI.cpf, CLI.celular, CLI.data_nasc, CLI.genero, CLI.data_cadastro, CLI.status, CLI.id_socket, ATEN.mensagem, COUNT(ATEN.mensagem) AS novas_mensagens, SUM(COMP.valor) AS valor_total, COMP.data AS ultima_compra, ARQ.nome AS foto, ATEN.data_mensagem
FROM ut_clientes AS CLI

LEFT JOIN ut_compras AS COMP ON COMP.id_cliente = CLI.id
LEFT JOIN ut_arquivos AS ARQ ON ARQ.id_tipo = CLI.id AND ARQ.tipo = 'ut_clientes'
LEFT JOIN ut_atendimentos AS ATEN ON ATEN.id_usuario_envio = CLI.id

WHERE ATEN.id_usuario_envio
  AND NOT EXISTS(
    SELECT ATEN.id_usuario_envio
    FROM ut_atendimentos AS ATEN2
    WHERE ATEN2.id_usuario_envio = CLI.id
    AND ATEN2.data_mensagem > ATEN.data_mensagem
  )
GROUP BY CLI.id
ORDER BY ATEN.data_mensagem DESC

I do not know if the idea was clear, but anything just ask me, I would appreciate if someone could give a light kkk

Thanks!