Noel - you could write to the mother by registered post, keep a copy for yourself, stating that you have tried to pay maintenance as agreed, money has bounced back to your account, and you will continue to put aside the money into an account yourself until such a time as mother provides you with account details or alternate method of passing money along.
That way if you get taken to court you will have your letter showing you tried to rectify the situation and details of whatever account you open to put the money into showing that you have continued to put the money aside. Perhaps if you opened the new account in your childs name that would be best?
Im not sure if the above letter would be better coming from you or solicitor but certainly if the situation is laid out on paper and sent registered and there is proof of an account opened for your child you have covered your obligations.