[dchftcs]

Not a lawyer but it can potentially be argued that the T&C were signed under duress and therefore void.

[halJordan]

You agreed to allow them to change the terms the first time you agreed

[dchftcs]

Not even their lawyers believe that for a second. If they did, they wouldn't have had to ask you to reaccept.

[ternaryoperator]

Yes, they’re allowed to make changes and you can either accept them (the matter being discussed here) or refuse them. But you do need to be given the option.