Bale, who left Real Madrid this week after seven years and joined former club Tottenham Hotspur on a season-long loan, won 13 trophies in the Spanish capital but was often scrutinised in the media for playing golf.
"This country, Great Britain, should be very proud of him and stop knocking him and write what he's done and what he's achieved," Bale's agent, Jonathan Barnett told talkSPORT: "And it's very annoying, and it's the same with Real Madrid, what he's achieved for them, they should be kissing the floor that he walks on."
Bale, 31, won the Champions League four times, two La Liga titles and three FIFA Club World Cups, as well as other trophies; and scored 105 goals in 251 games.
He was frozen out and started in just 14 games last season for Madrid amid reports of a difficult relationship with coach Zinedine Zidane and the club fans.
"For somebody that has achieved what he has achieved for the club in seven years, he should have been treated better," Barnett told the BBC. "I think what the fans did was disgraceful and the club didn't help. He could have been treated better and I'm very upset that he wasn't."
Bale almost moved to Chinese club Jiangsu Suning last summer before the move was called off at the last-minute by Madrid.
"I'm not going to put blame on people because it doesn't help," Barnett said. "In my opinion, he wasn't treated correctly for somebody that has done so much for a great club. I think things were wrong. It was an unhappy period of his time."
Bale's contract with Madrid expires in June 2022 but the option to remain at Spurs beyond next summer is open.
"This is the club he wants to play at," Barnett said. "I don't see any problems if he wants another year.
"He has a year left [after next summer on his contract with Madrid] so we have to see but hopefully the subject [of returning to Real Madrid] won't come up. He'll be so successful at Tottenham, he'll want to stay and it will be a simple deal to do the rest.
"I've looked after Gareth since he was a young boy and to see the smile back on his face was fantastic for me, it was special."