i will definitely wont be forking out any money for windows 10, i rather downgrade to my precious windows 7, im on phone to Microsoft now, will update this thread with the outcome.

Same with me, replaced my HDD with SSD and called up microsoft on phone and the agent used a new code to activate windows 7.
i still have the code and also the key to my windows 7.

The HDD on my PC gradually died in february, i replaced it with an SSD and activate windows 7 via phone.
If that is the cause of the problem, what is the solution please?

I'm experiencing the same problem like you, upgraded my windows 7 professional PC since july 29th and can't activate it.
Product key blocked. Error code: 0xC004C003, several calls to microsoft...