Very poor service

so furious about this company, they say i owe them 12k which i did not even use it, did not purchase from them for passed 3months. On their statement it shows a purchase that was made with them twice in 1day which does not make any sense how can a person buy for 2646 and later buy for 6899.65 how can 1 person buy for almost 10k in one day? On top of that i did not receive any message of purchase, what surprises me more is that the card is with me. The people who are ****ming us ate within the company