Hi Debbie,
The people who answer the DWP phones have no influence on any decisions regarding when you might be reassessed. Phoning to ask for your 'prognosis' should not have any adverse effects.
In theory all ESA awards are open ended, they do not come with a fixed term like DLA/PIP. In practice, the prognosis will be entered on the computer and it would be unusual to be assessed before this. However, recently there has been a huge backlog of cases and many routine reassessments were suspended, with the result that some claimants are waiting much longer than expected before reassessment.
Nothing on this board constitutes legal advice - always consult a professional about specific problems