Being billed for services NOT rendered

In 2021 I had recently bought my property & expereiencing alot of plumbing problems. I was using Bettafix Plumbing regularly & paying promptly for their services. So they had recently come to work on my geyser & they left my taps dripping so I called them again to come & fix the taps they had left dripping (there was nothing wrong with the taps before then). So they come out & tighten the dripping taps, they also had to work on the mosaic which was loose on my shower floor but after checking the shower floors they (Bettafix guys) advised me to rather redo the whole shower floor since all the mosaic was loose anyway. This was going to be a job for another day & I needed a quote for the cost. Long story short I receive an email with the invoice in which I'm being billed for lifting of mosaic & for fixing dripping taps. Mind you they had left the taps dripping during another job & the mosaic was not lifted because they advised me to redo the entire shower floor & were gonna quote me on that 🙄. Innitially they were to replace the loose mosaic tiles which was not done following their inspection & recommendations. Now they are threatning to hand over my account & possibly blackist me for not paying this account. I have emailed them back in 2021 explaining the reasons as to why I was not paying this invoice & asking them to adjust the invoice accordingly so I can pay for the invoice which they have failed to do & have now instead resulted to threatning me with legal action. They have never ever bothered to respond to my concerns with their billing. I still say I do not mind paying the invoice so long as they remove charges for work not done & for fixing their own mistakes.