Kitchen fitters

Fitting kitchens is usually a nightmare, in theory everything should fit but it never does, making adjustments so that everything matches takes skill and can be very time consuming.
All that is assuming all the parts have been delivered, if Wickes have priced a “fitted” kitchen you have probably paid a deposit and the balance on completion. More likely they have recommended a fitter with an “ estimate” not a quotation.

Look on your local checkatrade or similar to see if they are on there

Evie I dont have experience of these kitchen fitters but I think you need to look at your arrangement with Wickes.
If the price you paid to them included all the kitchen fitting, you should not need to pay out any more.
But ... if you were only recommended to these fitters, then you will have to pay the full cost.
If that is the case, you should certainly look around and get quotes to compare.
Hope this helps.