If you have C2 & FI actions on an EICR, then these are likely to require notable re-work to remedy.

To that end the organisation undertaking the remedial works should provide an Electrical Installation Certificate (EIC), or Minor Electrical Installation Works Certificate (MWC).

These when combined with the original EICR should provide evidence that the installation is now satisfactory.

You are welcome to ask the contractor to undertake or issue a satisfactory EICR, but this could attract further work and costs, depending upon the time between the initial EICR & the completion of the works, and the parties involved.

The IET and electrical schemes do not specify a time period for remedial works.

The description for C2 given in BS 7671 is:

"For items classified in Section K as C2 ('Potentially dangerous'), the safety of those using the installation may be at risk and it is recommended that a skilled person or persons competent in electrical installation work undertakes the necessary remedial work as a matter of urgency."

For FI it is:

"Where it has been stated in Section K that an observation requires further investigation (code FI) the inspection has revealed an apparent deficiency which may result in a code C1 or C2, and could not, due to the extent or limitations of the inspection, be fully identified. Such observations should be investigated without delay. A further examination of the installation will be necessary, to determine the nature and extent of the apparent deficiency (see Section F)."

The timescale for remedial works may well be stipulated by the business insurer, however.

I don't think you do have to have them return once work has completed. I've been led to believe that the report is the certificate. Please correct me if I'm wrong. 

Sammy