visas – Regarding sending passport to CVAC from (FEDEX)

I read on one of the websites that prepaid return envelopes from ups or usps are only accepted and other companies(Fedex) are not accepted for returning!!.Since I paid the amount and the labels i got are from FEDEX, how and what shall I do for the next process.I havent sent my documents yet. If VAC does not accept FEDEX envelopes while returning back to me then on what basis should I be sending the documents from FEDEX. Is there any other way for it.