Underpayment of UC

Hi me and my partner claim uc as a couple and recieve fortnightly payments and our statement for the 20th April says the amount we should recieve after all deductions which is £427 but we only received £360 but the uc say 427 was what we was payed but that isn't correct I have tried to contact them but keep getting the same old we will contact the case worker this has been said 3 times over the last week with no response can anyone advise me thank you in advance?