My first cruise with MSC was with Opera to Norway in 2013, and parted with £10 to get one of those "vouchers" for on board credit. I booked my next cruise that same year and was told to forward the voucher to the office - only to have it returned a couple of weeks later with the excuse "because I was getting a zero supplement as a solo traveller, I was not entitled to use the voucher." The MSC Agent who sold me the voucher knew I was a solo traveller as we had discussed future options for me.

 

Seems like MSC are not being "customer friendly" in their dealings with regard to these vouchers.