"I very rarely look at the emails but I just happened to glance at it and notice it had doubled," he told the Herald.
However, he wasn't surprised to receive the next email from AMP saying "we made a mistake".
"It just goes to show that if something seems too good to be true it usually is."
Wilks wondered if the provider had possibly been hacked, or the victim of fraud.
However, in responding to questions, AMP said it was an issue in the design and production of the email newsletter only and not with any of its core systems or data.
"At all times, clients' funds were safe and they could view their correct account balance through our My AMP app and portal," it said.
"Unfortunately, sometimes mistakes do happen, but we have taken steps to prevent this from happening again."
Wilks said while that was a relief, it would be more reassuring if the provider didn't make mistakes.
"I just hope they don't do it again."
AMP said it had emailed and phoned clients to apologise.