Please help me,I wrote a letter to the seller,

[jolitab2016]

I wrote a letter to the seller, Hello sorry I didn't look at the size of the shirt would I be able to cancel the order sorry. An agreement with the seller could not be reached, please help me.   Thanks

[plpmr]

as the seller is a registered business seller you have the legal right to cancel - tell them this and if necessary you can involve trading standards.