Hi Welcome to JustAnswer.
You do not need to send your T-shirt to them generally as per replacement policies of most of the companies , they will collect T-shirt from you and either give you new one or refund your money.
Please let me know from where you have purchased it ?
Which website ?
You have to hurry up as generally all the websites have 7 days replacement guarantee.
If required, I can remotely connect to your PC and do this for you .
I would need a name of website where you have made payment without knowing where you have made payment and from where you have purchased it, I won't be able to help you. Please check your emails you must have got an email from them about order confirmation. Please copy paste that email here in this chat box.