Question for Intercity STC Coaches Ltd.

I bought 2tickets from Tamale branch to travel to Kumasi on Monday 17th July, 2017 at 6am, but i am currently in Bimbilla and can't make it to Kumasi on Monday but Tuesday, so i want to find out if something can be done about it. I have tried reaching you on ur office line but no one is picking up.
Please help me.