Just an update that I've managed to work out a solution with them.
On the positive side, each time I wrote in (using their site's contact us form), I've always received replies within 12 hours. This is a huge plus. They have also been willing to work with me to find a flexible alternative.
As they have verified with their factory, the shirts have indeed been altered, thus leaving the marks. So they no longer require me to resend the items back. They've told me that the practice to send items back is to show the mistakes to the production team so that it will not be repeated. As a young company, I'm sure this is part of the learning curve.
I cannot say for certain how the quality will be until I receive my replacement from them. I'm sure though, a lesson will be learnt, and hopefully that benefits anyone else who might be placing orders with them in future.
As it stands, customer service is good. I wish they had just gotten things done right the first time round. I will decide if I still want to continue my dealings with them after the 2nd batch, a major advantage over Jantzen is their customer service, timing of delivery and a very easy to use website.