moving number from ID sim only to ID pay monthly

I have had an ID sim only contract for almost 12 months. I have just ordered a new monthly contract with ID mobile and a separate sim only deal for my son to use with my old handset. I ordered these separately from the ID app so they don’t show up on my app account. I put the new sim in the new phone but I want to cancel the old ID sim only deal and move the number from that onto the pay monthly sim. I requested a PAC code but I don’t think that was the right thing to do. Both SIM cards work currently but I don’t want to pay for the old sim only deal whilst I pay the two new sims I have purchased. What should I do?