10 visits and no sim swap done

My phone was ****** about 3 weeks ago and I have been trying to get a sim swap done ever since then with no success. Been to Cresta & Bright water commons and either they are offline or have no stock!! Took off time from work, sacrificed my lunch time only to be unsuccessful at getting one sim swap done! Just been to brigh****er commons few minutes ago and the guy was just like sorry they offline, asked him to provide me with a contract sim so I could get it done telephonically with the call centre (as advised by call centre last night) only for him to tell me it doesn't work that way and it needs to be done in store. While I tried to get the call centre on the line, he tells me there is no stock and then he wasn't interested in assisting me any further. I don't understand how difficult can it be to get one sim swap done. I need my sim and I am making no further trips to your non-competent stores. I don't care how but you guys need to make it happen and get my sim card to me. I am done. I haven't got the time to run up and down like a headless chicken. Get back to me ASAP with details on how this will be rectified. While we at it, also advice me when I can cancel both my contracts.