This was a major challenge Nigeria's Crypto community faced which forced crypto traders to revert to the old way of buying and selling commonly known as "Peer to Peer (P2P)".

Several popular exchanges have implemented the P2P feature on their exchange. A typical example is Quidax which launched it's P2P platform weeks back.

Details can be found here : https://blog.quidax.com/make-way-p2p-is-live-on-quidax/