Hi Abdessamad,
can you please share how are you replicating purchase request to from ECC to SRM? Are you using RFC (SRM 5 and older releases) or XML (via PI - SRM 7 onwards) or CPPR?
I am really surprised about the behaviour you are describing. The thing is that product category gets replicated 1:1 from ECC to SRM. In case that technical user does not have proper authorizations the replication should fail. There could be some BAdI/s active but it depends on your answer to my first question.
BTW: are you sure that the SC is created from the PR you are talking about?
(check relations in BBP_PD)
Best regards,
Tomas