Can't activate sim card

Hello,

I have just moved from Android to iPhone and I needed a smaller sim card, so I bought the SIM card activation kit from my boost local store and asked them to keep my phone number. After inserting the card in the iPhone, I tried to activate the new sim card as a existing customer but it says: db_no_data_found_exception-Client. [series of number] is not found in NMS.

What can I do?