Change Naira to Euro (Abuja)

Hi,

Even though I've been around in Nigeria now for many years, I just can't get my head around the whole changing scheme.

I get an allowance in Naira's. Some of that I want to convert into euro's on my bank account and either use it to transfer or in this case use it to buy some goods from Europe.
For some reason that I can't understand bank are not allowed to change currency. Even though the signs show their exchange rate, which at the time of writing is around Protected content , I keep on being told I need to buy it on the street.

I can't seem to understand how that would be the 'normal' or 'legal' way of doing things. On the street euro's are being sold at around Protected content , substantially higher then the actual rate. Especially considering that 'street-rates' are usually better then bank rates, not worse.
Result; I'm not changing, not buying products (importing) and though not stimulating the economy.

What am I missing? Where should I change money to the normal daily rate, like in civilization?