cancel my contract and give me a letter for sim swap....i want ti be on prepaid.....regret ever doing business with u

i have been strugling to cancel a 6 month contract from de 1st month that was in july 2014. each time i call im told il be called back but nothing ever happens. i lost my phone mid july 2014 to date im still unable to get a letter for a sim swap and losing a lot of business as clients are unable to reach me. i want a letter for a sim swap and de contract to be cancelled. very bad service and unreliable company