The clause as drafted ("This agreement can not be cancelled by the client") seems rather odd for at least a couple of reasons.
First, an onerous termination clause might limit in what circumstances one or the other party can terminate a contract, prescribe precise procedures for doing so (including notice periods), and include compensation for cancellation/termination. But the clause as drafted seeks to go beyond that, to actually prohibit cancellation.
Second, in common law there is a right to terminate for a repudiatory breach by the other party. This right cannot be written out of a contract.
As Rod says, tread carefully, and be sure to read your contract in full before you decide upon any action.