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You maybe able to find a sim card plastic adapter on eBay that your current sim card will fit into to make it bigger.
Which model of Nokia is it may I ask.
Some £1 discount stores also sell sim card adapters as well as the network stores.
Sorry, I should've explained.... I currently have an old style SIM card in my phone that works ok but for personal reasons I need a new number and just want to get a new SIM. Those 3 in 1 micro sims break when I try and put them in and take them out so wanted an old style one but am finding it almost impossible to track one down as everywhere stocks the new style ones.