Open-source, on premises, CRM with Whatsapp integration

Hello CRM Experts…

I'm studying CRM possibilities for a small company. What they need is something that can run on premises, preferably on a docker (the database, the client program would run on windows 10 machines), open source, preferably free or freemium, that would integrate with the Whatsapp API.

They have multiple cellphone accounts and they keep sending clients between them, it is a mess… I proposed a single point of communication, because the client do not need to know the number of accounting, sales, support, etc… and to put all the communication on the main number of the company. it is a small company, around 6 persons, they do not have the budget for anything more than the ERP.

I need your help, most searches just send me to way too expensive (for this small company) solutions