Supplier collecting and paying taxes on transaction attracting RCM cannot relieve the recipient from RCM liability. However, there are few case laws in ST regime wherein they says, as there is no revenue loss to govt., no need to pay again under RCM.
Its better to make a decision whether to pay again under RCM or not..
Henceforth, do not pay GST to GTA though he is charging @ 5% but pay under RCM.