Declined for no reason

Ive app**** for a pick n pay credit store account on the 17th july and it was approved on the 18th...i went the wednesday to pick n pay to purchase a few stuff and the transaction went thru but today my transactions was decline reason 39: no credit account ...what makes me furious is i still have available credit. Cause its the second time im using my card...and to be decline knowing well you have credit available is embarrasing very dissapointed