Sometimes your mpesa account may get blocked. If your mpesa account gets blocked but you know the pin, you can get it unblocked by following some simple steps.
From the line dial *100# for prepaid and *200# for postpaid
select 4 for mpesa
select 2 mpesa information
select 7 PIN unlock
This will unlock you mpesa account
In case you mpesa is locked because you have forgotten your password, follow these steps to unblock How to recover a lost Mpesa PIN