It appears that the parties varied the terms of the original contract in view of their inability to perform it due to the Covid-19 global crisis and national “lockdown”. The fixed term has been moved back a few months while the contract is “on hiatus” rather than terminating it.
Variations to commercial contracts must be agreed by both parties to be effective, otherwise the party attempting to impose and enforce the variation unilaterally is committing a breach of the contract.
In your case, both parties appear to have expressly consented to the first variation of the contract and to abide by the new term. However, the other party is now in breach of contract by its attempts to renege on the new term of the contract and re-introduce unilaterally the original term of the contract.
You now have two options.
You may either terminate the contract immediately for actual and/or material and/or repudiatory breach of contract by the other party. You may then claim damages for breach of contract in the civil County Courts for damages for your losses, such as fees you have paid above what was originally agreed.
Otherwise, you may waive the breach, affirm the variation by reverting to the original terms and continue the contract as the other party desires.