Qt Software can say what they want but according to me you are the owner of the code so you can re-licence whenever you want. At worst you will change the application name and/or release a new version of the software.

and also is it true that when i will be using lgpl qt then i have to make all the library link dynamic(qt libraries) and make the source code of those library open source
Yes, you can't link LGPL components statically in closed-source applications. You don't have to provide the source code for LGPL components as long as you don't modify their source.

and i also have to give away the object file of the program without the source code that i have written(i am not changing the qt library)
No, this you don't have to do. Your application is still closed-source and licenced the way you choose it to so you are not obliged to share its code (neither source nor binary) with anyone.