Can one instruct their broker on the minimum amount that can be transacted in their account in a single transaction/trade? This mainly to control the transaction charges! Some brokers have gone rogue and execute trades that result upto 15% fee. Case in point is selling of 100 Mumias sugar shares despite ordering a sale of thousands of them.
Kindly assist on how I should go about this.

Why cant you just move to a broker who has an online platform and make your rules?

You need to understand percentages. Charges are levied as a percent of sale. Some brokerge firms have a maximum number where they will give a discount for a buy or sale for a certain amount say they may charge a commission of 2.0% for 100000 or more and 2.1% for less than 100000.
Also note that what you tell them to sell is not bought buy another buyer wholesome but they sell to different buyers in bits within a period of time depending with the market unless you take a buyer who is willing to buy all what you are selling. This is one reason we see odd shares hard to sell. If I want to buy 2600 shares of mumias, the broker may get these shares from different willing sellers in batches of 800, 1200 and 600. The percentage commission charge from each must add up as if it was done from one seller.

Ever heard of 'computer error'? but it can be reviewed on demand!

CFCFS

I feel conned by my broker buying a batch at less than 800 shillings then charging commission of over 100 bob. I'm just not allowing this. Unfortunately, the only way I can contact them is via email. So far no response.

Despite the amount involved is very little but it is these little overcharged amounts from several clients that make them millionaires. My fees have never truly been reflected on those percentages. In this case, the broker purchased shares worth 790 shillings and charged me 104 shillings. Shouldn't that have been 16.60 bob. They never mentioned any other fees so I believe the only fee is the 1.8% and 2.1% depending on the transaction. I'm now demanding a whole review of my statement. The day I noticed this few shillings conning, I stopped injecting more money into my account. I will definitely write to CMA if no proper explanation come forth.
NB: I never ordered anything that much. It is what they sold. My order was way higher.