Poor reception after good reception for 2 years

I have had my Galaxy S6 for 2 years. A couple weeks ago I suddenly started having very poor reception. I took it to AT&T and they replaced my sim card and reset my mobile network connection and it still didn't help. The rep said that the antenna is likely worn out. They tested it and it was getting really poor reception compared to 2 other phones in the store. Can an antenna wear out? Anything else that could cause this sudden issue with reception?