Archie, some of the articles I’ve read suggest using less fertilizers especially nitrogen to allow the tomatoes to grow slower allowing more time for them to absorb the calcium.
I had BER my first year of gardening, saved that harvest by picking off all the lower tomatoes and top dressing my plants with a ring of crab shells around each base (look up Neptune crab shells) and sprayed the plants with Miracle Gro every two weeks or so for the remainder of the season.
Since then I have planted mostly smaller or medium sized varieties with a few larger ones instead of mostly larger ones - less demand for nutrients. My beds are mainly leaf compost, sterile cow manure, crab shells, no more Miracle Gro the last two years. I keep the bottom foot of my plants completely trimmed of branches and above that just trim the sucker branches off - same with my peppers. Again allowing the nutrients to be more available to the fruit.
Another thing to consider, try to choose varieties that yield at different times of the season if possible, spreading out the demand for available nutrients time wise.
Try green sand or azomite. They might need more than the calcium.
And something that’s got micro-organisms too if you can find it.
You didn’t give many specifics about fertilizer. Sometimes trace elements are needed for the plants to be able to take advantage of the calcium.
You may need to take a soil sample to determine what is going on. Best bet is to contact you county University Extension office for help with that - cheap way to go.
I have always used bone meal, Epsom Salts, along with ground up eggshells, to fight it in container plants.