Phone call from ESA

hi

I’m new to this group and this is my first post. Could I please have some advice if possible.
my husband gets esa and pip and in a support group. Today he got a phone call from work and pensions saying he might need to send them bank statements from 2023 to present day. They wanted to know if he had any saving which he doesn’t. He took some of his private pension but made sure it was under the amount he was allowed. That money has now gone. I also told the esa and housing benefit that he was taking out some of his pension and they both told me as long as it was under £6000 then he didn’t need to inform them. Does anyone know why we had this random phone call. They said if they do need the bank statements then they will get back in touch. Don’t know what to think now.
many help would be very much appreciated.