Big Price Hikes; Threatening

I have stored with Stor-Age for 1.5 years. In that time, they have increased storage costs by over 30%. A recent cost increase I neglected to pay, as an oversight, they agreed to me paying the following month and made a note on my account. Despite this, they app**** a ZAR 200 penalty charge, I remind them of what was agreed. They then start sending Rights of Lien over property, letters of threat and auto-email telling me how to give notice over a ZAR 340 shortfall over a much larger monthly amount that was settled on time. You would think they would be a little accommodating after proportionally large price hikes and not go back on their word as I have paid every month, without fail. You decide what is ethical and whether they treat their customers well.