Many thanks for your patience, I am pleased to be able to continue assisting with your query now. I note you said you do not need any help but I will provide an answer anyway and it may come in handy still.
I assume you are asking about the legality of such a contract being entered into by a relief manager who has not directly employed by the company. In that case, it would not make the contract automatically invalid or unenforceable, as the main consideration is whether that person had the authority to enter into such contracts in the first place. It could easily be the case that someone is not directly employed by your company, but they are given the authority to make certain business decisions and even enter into contracts on behalf of the company. It will very much depend on what their authority was and what you had authorised them to do. Even if you did not specifically mention that they can enter into such a contract, a relevant factor would be whether a person in that job, if employed directly, would normally be able to do this.
If it is clear that they had no authority to enter into such contracts and they went way outside of what they were authorised to do, you could potentially try and challenge this as being an invalid contract. The issue is that only a contract can determine if this is the case, assuming the provider is not willing to accept this.
Hopefully, I have answered your query in a way that is simple and easy to understand. If anything remains unclear, I will be more than happy to clarify it for you. In the meantime, thank you once again for using our services.