The average time of treatment and validation of a payment by cheque is 2 days maximum after reception of your mail and cheque.
You sent your payment there is less than 7 days: have patience, your payment undoubtedly did not reach us yet.
That made more than 10 days, check near your post office so disturbances can explain this delay. If it were not the case, thanks for agreeing to contact the Customer service so that one of our advisers solves your case.