Cathy, if you want to try and see if hydrogen peroxide works, get the 6% solution from the chemist, it's very cheap, 100ml usually in a dark brown bottle. Put some gloves on, pour a little into the lid or an eggcup and apply with a well soaked cotton wool bud. If it works on your grout you should see it almost immediately, don't leave on longer than ten minutes, rinse it off thoroughly, pour the used solution down the sink (perfectly safe) followed by water, rinse the lid or the eggcup well, and keep the rest in your medicine cabinet as a throat gargle (instructions usually on the bottle) and to remove fruit juice stains etc.
Don't dip the cotton wool bud directly into the bottle, as you won't be able to use any of it afterwards.
If the peroxide doesn't work I'd have it redone keeping the copper reaction in mind.
And let us know how you got on!