Complex sentence: It has been widely reported since 2009, that Swiss authorities froze a seven billion US $bank accounts of his on the pretext of irregular transactions, which led him to engage in a legal battle to realize his frozen money deposited in these banks.
Split into simpler sentences: It has been widely reported since 2009, that Swiss authorities froze bank accounts of his worth seven billion US $, on the pretext of irregular transactions. This led him to engage in a legal battle to realize his frozen money deposited in these banks.