unmanaged to managed, new tenancy agreements issued costing us £250ish each...

Tenancy Types and Management

My sister and I at first managed our mother's house in Salisbury, 90mins drive from each of our homes but that was where mum lived. Then we decided to put it in the hands of an agent to manage, my sister mostly spoke to the agent and agreed it but I see on this month's statements each tenant was issued with a new tenancy agreement at a cost to us of £400 each, so we have no profit this month. We can cover the costs but this extra requirement was not discussed with either of us prior to set up, we just got landed with it, and the agent seems to change staff with alarming frequency. Is this standard practice and if so why?