Is it common practice to threaten your customers?

I have multiple business accounts, including one at FNB. I withdrew most of the money from it a while ago and have just been holding it in case I use it again for another business of mine. I am a model customer. So I was surprised to get an email telling me that I am in arrears. When I checked it was to the amount of just under R90. Obviously due to bank fees that chewed up the last remaining money in that account. Things like that happen. But instead of getting an email from FNB notifying me nicely of this fact, I get an extremely threatening one stating the following (please note that this was the first ever correspondence I received from FNB about this): That I am in arrears of said amount and if I do not settle it within 30 days FNB will close the account, I will be handed over to your attorneys and I will be fully liable for the attorney fees. Wow! Seriously FNB? Well, just so you know, I made a payment into that account (something I would have done regardless when I noticed that your ridiculous fees that you charge used up the buffer money in the account). But note this: NEVER threaten me again. I will take my business elsewhere. Learn some manners! My 1 year old has more...