Yeah that code would be the "PAC" code needed to switch the details over more than likely.
Honestly if they give you the run around again you could always try one of these
It can cut your existing SIM to fit newer phones.
I would suggest asking one of those mobile phone repair shops as they sometimes have one and charge like a quid to cut one for you but I'm not sure if they're even open.
If you travel a lot, you can buy a cutter Universal 3 in 1 / Standard Sim/ Micro Sim/ Nano Sim Card Cutter For iPhone 7 6S 6 5S 5 4S 4 Plus Samsung S5 S6 S7 Sony Huawei Motorola and other Smartphones incl. 3 SIM Adapters + 1 SIM Card Eject Pin MMOBIEL https://www.amazon.ca/dp/B01MDNZ1PV/ref=cm_sw_r_cp_api_81TnzbJCCFRM5
MMOBIEL Universal 3 in 1 / Standard/Micro / Nano Sim Card Cutter incl. 3 SIM Adapters and 1 SIM Card Eject Pin https://www.amazon.com/dp/B01MDNZ1PV/ref=cm_sw_r_cp_api_glt_fabc_NS36R7DXAHPCBBD3QF0P