C# Multiple Generic Parameters into single concrete type

I am little stuck with achieving something with multiple generic parameters. I have a service interface which will take a messagecontext interface as input to method.

 public interface IService<T,U> where T : IMessageContext<U>
 {
    void ExecuteJob(T data);

    bool CancelJob();
 }

Then an abtract class which implements the interface.

public abstract class AbstractService<T,U> : IService<T,U> where T: IMessageContext<U>
{

    public virtual bool CancelJob()
    {
        return true;
    }

    public abstract void ExecuteJob(T data);
}

The IMessage interface and default implementation is as shown below

public interface IMessageContext<U>
{
    U Data { get; set; }
}

public class DefaultMessageContext : IMessageContext<string>
{
    public string Data { get ; set; }
} 

In this case, if we inherit the AbstractService class, it would be like below with the Generic parameters for T as DefaultMessageContext & U as string

public class ConcereteService : AbstractService<DefaultMessageContext,string>
{

    public override void ExecuteJob(DefaultMessageContext data)
    {
        //Execute the job
    }
}

Is there a way where I can just only mention the type for T as DefaultMessageContext as the type of U is already set in the class while implementing IMessageContext

Something like this

public class ConcereteService : AbstractNewService<DefaultMessageContext>
{

    public override void ExecuteJob(DefaultMessageContext data)
    {
        //Execute the job
    }
}

I could introduce another layer of abstraction where the type of U is set as string and only keep T open for implementation like AbstractStringService<T> : AbstractService<T,string>. But I don't want to do that.

Is there any other way to achieve it.