The telephone number 03456032821 has been identified as a scam number used to send scam HSBC phone calls and fake HSBC texts. If you receive any type of communication from this number then you should ensure that you do not answer the call and do not open any links.
Recipients of calls from this number have reported being asked security questions regarding their bank account. Others report receiving a call from 03456032821 and then being asked about their mortgage. In essence the caller is flapping around trying to find something that is relevant to your account. They are a scammer. Hang up.