I get it.You applied online and that is why they have probably asked to bring original challan.
I think you shoulf contact SPSC tomorrow in the morning if their office is opened.

Head Office
Thandi Sarak, Hyderabad, Sindh
Phone # 022-9200694, 246
Fax # 022-9200697
email: info@spsc.gov.pk

Regards

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You are not Obligated to succeed,You are Obligated to try ( Winston Churchill )