A written warning is the first step
You have to proceed in stages
I had one of those. He simply said he had no money. A written warning had no effect. At the time I knew a retired murder and robbery detective. Just before the 3rd month was up, he went to have a word with the tenant. He and his wife left during the following month. The neighbour to the flat told me that one Saturday morning a bakkie arrived and they walked out with their stuff
You can Google/AI the procedure to follow and the wording for letters etc but after one month of no payment is made after following procedure, best is to just send a builder to go there with spare keys and say “urgent maintenance”. Then proceed to remove all entrance doors to the house and disable the electricity connection.