Worst service provider ever

I am completely unhappy with Rain and their service. I app**** for their 4G SIM card in January 2022 and the service was so bad that I cancelled in July 2022. Now recently I received a call and messages to tell me that I must pay an outstanding balance or else “they will take action”! Now my concern is that why only after a year do they claim that I owe them an outstanding amount? Why didn’t they communicate this last year immediately after I cancelled their service and why is it so hard for them to send me statements to prove that I really do owe an outstanding amount?